On; -- used in all the senses of that word, with which it is interchangeable. Chaucer. [1913 Webster]
" Upon conveys a more distinct notion that on carries with it of something that literally or metaphorically bears or supports. It is less employed than it used to be, on having for the most part taken its place. Some expressions formed with it belong only to old style; as, upon pity they were taken away; that is, in consequence of pity: upon the rate of thirty thousand; that is, amounting to the rate: to die upon the hand; that is, by means of the hand: he had a garment upon; that is, upon himself: the time is coming fast upon; that is, upon the present time. By the omission of its object, upon acquires an adverbial sense, as in the last two examples." [1913 Webster]
"Our host upon his stirrups stood anon." [1913 Webster]
"Thou shalt take of the blood that is upon the altar." [1913 Webster]
"The Philistines be upon thee, Samson." [1913 Webster]
"As I did stand my watch upon the hill." [1913 Webster]
"He made a great difference between people that did rebel upon wantonness, and them that did rebel upon want." [1913 Webster]
"This advantage we lost upon the invention of firearms." [1913 Webster]
"Upon the whole, it will be necessary to avoid that perpetual repetition of the same epithets which we find in Homer." [1913 Webster]
"He had abandoned the frontiers, retiring upon Glasgow." [1913 Webster]
"Philip swore upon the Evangelists to abstain from aggression in my absence." [1913 Webster]

upon, prep. = ON.

Usage:
Upon is sometimes more formal, and is preferred in once upon a time and upon my word, and in uses such as row upon row of seats and Christmas is almost upon us.

Etymology:
ME f. UP + ON prep., after ON upp {aacute}

N  different time, other time, aorist, aoristic, indefinite, at that time, at which time, at that moment, at that instant, then, on that occasion, upon, not now, some other time, when, whenever, whensoever, upon which, on which occasion, at another time, at a different time, at some other time, at any time, at various times, some one of these days, one of these days, one fine morning, eventually, some day, by and by, sooner or later, some time or other, once upon a time.

act upon, agreed upon, alight upon, bear down upon, bear upon, blunder upon, borne in upon, build upon, burst upon, chance upon, come upon, coming upon, comment upon, depend upon, descend upon, embark upon, encroach upon, enter upon, expanding upon, fall upon, fasten upon, fawn upon, feed upon, force upon, frown upon, gain upon, happen upon, hinge upon, hit upon, impose upon, insist upon, light upon, look down upon, look upon, marched upon, obtrude upon, pounce upon, presume upon, prevail upon, put upon, reflect upon, set upon, settle upon, spring upon, stumble upon, supervene upon, swoop down upon, touch upon, tread upon, upon one's guard, visit upon, wear upon, weigh upon

   Once. Chaucer. [1913 Webster]

1.  guard(n = noun.person) - a person who keeps watch over something or someone;
is a kind of defender, guardian, protector, shielder
has particulars: bouncer, chucker-out, door guard, doorkeeper, doorman, gatekeeper, hall porter, ostiary, porter, halberdier, screener, security guard, watcher, watchman
Derived form verb guard₁

2.  guard(n = noun.person) - the person who plays that position on a football team; "the left guard was injured on the play"
is a kind of lineman

3.  guard(n = noun.artifact) safety, safety device - a device designed to prevent injury or accidents;
is a kind of device
has particulars: fender, safety catch, safety lock

4.  guard(n = noun.attribute) - a posture of defence in boxing or fencing; "keep your guard up"
is a kind of attitude, position, posture

5.  guard(n = noun.person) - the person who plays the position of guard on a basketball team;
is a kind of basketball player, basketeer, cager
has particulars: oscar palmer robertson, oscar robertson, robertson

6.  guard(n = noun.group) - a military unit serving to protect some place or person;
is a kind of force, military force, military group, military unit
has particulars: bodyguard, home guard, territorial, territorial reserve
Derived form verb guard₂

7.  guard(n = noun.act) precaution, safeguard - a precautionary measure warding off impending danger or damage or injury etc.; "he put an ice pack on the injury as a precaution"; "an insurance policy is a good safeguard"; "we let our guard down"
is a kind of measure, step
has particulars: backstop, security, security measures

8.  guard(n = noun.act) guard duty, sentry duty, sentry go - the duty of serving as a sentry; "he was on guard that night"
is a kind of assignment, duty assignment
Derived form verb guard₁

9.  guard(n = noun.act) - (American football) a position on the line of scrimmage; "guards must be good blockers"
is a kind of lineman
is a member of eleven, football team

10.  guard(n = noun.act) - a position on a basketball team;
is a kind of position
is a member of basketball team, five

1.  guard(v = verb.social) - to keep watch over; "there would be men guarding the horses"
is one way to follow, keep an eye on, observe, watch, watch over
Derived forms noun guard₈, noun guard₁
Sample sentences: Somebody ----s something; Somebody ----s somebody

2.  guard(v = verb.competition) ward - watch over or shield from danger or harm; protect; "guard my possessions while I'm away"
is one way to protect
Derived form noun guard₆
Sample sentences: Somebody ----s something; Somebody ----s somebody; Something ----s somebody; Something ----s something

3.  guard(v = verb.competition) defend, hold - protect against a challenge or attack; "Hold that position behind the trees!"; "Hold the bridge against the enemy's attacks"
is one way to protect
Sample sentences: Somebody ----s something

4.  guard(v = verb.social) - take precautions in order to avoid some unwanted consequence; "guard against becoming too friendly with the staff"; "guard against infection"
is one way to act, move
Sample sentences: Somebody ----s PP

1.  To protect from danger; to secure against surprise, attack, or injury; to keep in safety; to defend; to shelter; to shield from surprise or attack; to protect by attendance; to accompany for protection; to care for. [1913 Webster]
"For Heaven still guards the right." [1913 Webster]

2.  To keep watch over, in order to prevent escape or restrain from acts of violence, or the like. [1913 Webster]

3.  To protect the edge of, esp. with an ornamental border; hence, to face or ornament with lists, laces, etc.

4.  To fasten by binding; to gird. B. Jonson.

   To watch by way of caution or defense; to be cautious; to be in a state or position of defense or safety; as, careful persons guard against mistakes. [1913 Webster]

1.  One who, or that which, guards from injury, danger, exposure, or attack; defense; protection. [1913 Webster]
"His greatness was no guard to bar heaven's shaft." [1913 Webster]

2.  A man, or body of men, stationed to protect or control a person or position; a watch; a sentinel. [1913 Webster]
"The guard which kept the door of the king's house." [1913 Webster]

3.  One who has charge of a mail coach or a railway train; a conductor. [1913 Webster]

4.  Any fixture or attachment designed to protect or secure against injury, soiling, or defacement, theft or loss [1913 Webster]

5.  A posture of defense in fencing, and in bayonet and saber exercise. [1913 Webster]

6.  An expression or admission intended to secure against objections or censure. [1913 Webster]
"They have expressed themselves with as few guards and restrictions as I." [1913 Webster]

7.  Watch; heed; care; attention; as, to keep guard. [1913 Webster]

8.  The fibrous sheath which covers the phragmacone of the Belemnites. [1913 Webster]
" Guard is often used adjectively or in combination; as, guard boat or guardboat; guardroom or guard room; guard duty." [1913 Webster]

guard, v. & n.
--v.
1 tr. (often foll. by from, against) watch over and defend or protect from harm.
2 tr. keep watch by (a door etc.) so as to control entry or exit.
3 tr. supervise (prisoners etc.) and prevent from escaping.
4 tr. provide (machinery) with a protective device.
5 tr. keep (thoughts or speech) in check.
6 tr. provide with safeguards.
7 intr. (foll. by against) take precautions.
8 tr. (in various games) protect (a piece, card, etc.) with set moves.
--n.
1 a state of vigilance or watchfulness.
2 a person who protects or keeps watch.
3 a body of soldiers etc. serving to protect a place or person; an escort.
4 US a prison warder.
5 a part of an army detached for some purpose (advance guard).
6 (in pl.) (usu. Guards) any of various bodies of troops nominally employed to guard a monarch.
7 a thing that protects or defends.
8 (often in comb.) a device fitted to a machine, vehicle, weapon, etc., to prevent injury or accident to the user (fire-guard).
9 Brit. an official who rides with and is in general charge of a train.
10 in some sports: a a protective or defensive player. b a defensive posture or motion.

Idiom:
be on (or keep or stand) guard (of a sentry etc.) keep watch. guard cell Bot. either of a pair of cells surrounding the stomata in plants. guard-rail a rail, e.g. a handrail, fitted as a support or to prevent an accident. guard ring Electronics a ring-shaped electrode used to limit the extent of an electric field, esp. in a capacitor. guard's van Brit. a coach or compartment occupied by a guard. lower one's guard reduce vigilance against attack. off (or off one's) guard unprepared for some surprise or difficulty. on (or on one's) guard prepared for all contingencies; vigilant. raise one's guard become vigilant against attack.

Derivative:
guarder n. guardless adj.

Etymology:
ME f. OF garde, garder ult. f. WG, rel. to WARD n.

N  safety, security, surety, impregnability, invulnerability, invulnerableness, danger past, danger over, storm blown over, coast clear, escape, means of escape, blow valve, safety valve, release valve, sniffing valve, safeguard, palladium, guardianship, wardship, wardenship, tutelage, custody, safekeeping, preservation, protection, auspices, safe-conduct, escort, convoy, guard, shield, guardian angel, tutelary god, tutelary deity, tutelary saint, genius loci, protector, guardian, warden, warder, preserver, custodian, duenna, chaperon, third person, watchdog, bandog, Cerberus, watchman, patrolman, policeman, cop, dick, fuzz, smokey, peeler, zarp, sentinel, sentry, scout, garrison, guardship, refuge &c, anchor, precaution, quarantine, cordon sanitaire, confidence, protect, take care of, preserve, cover, screen, shelter, shroud, flank, ward, guard, secure, entrench, intrench, fence round, house, nestle, ensconce, take charge of, escort, convoy, garrison, watch, mount guard, patrol, make assurance doubly sure, take up a loose thread, take precautions, double reef topsails, seek safety, take shelter, find shelter, Adj, safe, secure, sure, in safety, in security, on the safe side, under the shield of, under the shade of, under the wing of, under the shadow of one's wing, under cover, under lock and key, out of danger, out of the woods, out of the meshes, out of harm's way, unharmed, unscathed, on sure ground, at anchor, high and dry, above water, unthreatened, unmolested, protected, cavendo tutus, panoplied, snug, seaworthy, weatherproof, waterproof, fireproof, defensible, tenable, proof against, invulnerable, unassailable, unattackable, impenetrable, impregnable, imperdible, inexpugnable, Achillean, safe and sound, scathless, unhazarded, not dangerous, unthreatening, harmless, friendly (cooperative), protecting, protective, guardian, tutelary, preservative, trustworthy, ex abundanti cautela, with impunity, all's well, salva res est, suave mari magno, a couvert, e terra alterius spectare laborem, Dieu vous garde, safety, security, surety, impregnability, invulnerability, invulnerableness, danger past, danger over, storm blown over, coast clear, escape, means of escape, blow valve, safety valve, release valve, sniffing valve, safeguard, palladium, guardianship, wardship, wardenship, tutelage, custody, safekeeping, preservation, protection, auspices, safe-conduct, escort, convoy, guard, shield, guardian angel, tutelary god, tutelary deity, tutelary saint, genius loci, protector, guardian, warden, warder, preserver, custodian, duenna, chaperon, third person, watchdog, bandog, Cerberus, watchman, patrolman, policeman, cop, dick, fuzz, smokey, peeler, zarp, sentinel, sentry, scout, garrison, guardship, refuge &c, anchor, precaution, quarantine, cordon sanitaire, confidence, protect, take care of, preserve, cover, screen, shelter, shroud, flank, ward, guard, secure, entrench, intrench, fence round, house, nestle, ensconce, take charge of, escort, convoy, garrison, watch, mount guard, patrol, make assurance doubly sure, take up a loose thread, take precautions, double reef topsails, seek safety, take shelter, find shelter, Adj, safe, secure, sure, in safety, in security, on the safe side, under the shield of, under the shade of, under the wing of, under the shadow of one's wing, under cover, under lock and key, out of danger, out of the woods, out of the meshes, out of harm's way, unharmed, unscathed, on sure ground, at anchor, high and dry, above water, unthreatened, unmolested, protected, cavendo tutus, panoplied, snug, seaworthy, weatherproof, waterproof, fireproof, defensible, tenable, proof against, invulnerable, unassailable, unattackable, impenetrable, impregnable, imperdible, inexpugnable, Achillean, safe and sound, scathless, unhazarded, not dangerous, unthreatening, harmless, friendly (cooperative), protecting, protective, guardian, tutelary, preservative, trustworthy, ex abundanti cautela, with impunity, all's well, salva res est, suave mari magno, a couvert, e terra alterius spectare laborem, Dieu vous garde.

VB  be safe, keep one's head above water, tide over, save one's bacon, ride out the storm, weather the storm, light upon one's feet, land on one's feet, bear a charmed life, escape, make safe, render safe Adj, protect, take care of, preserve, cover, screen, shelter, shroud, flank, ward, guard, secure, entrench, intrench, fence round, house, nestle, ensconce, take charge of, escort, convoy, garrison, watch, mount guard, patrol, make assurance doubly sure, take up a loose thread, take precautions, double reef topsails, seek safety, take shelter, find shelter.

VB  preserve, maintain, keep, sustain, support, hold, keep up, keep alive, refrigerate, keep on ice, not willingly let die, bank up, nurse, save, rescue, be safe, make safe, take care of, guard, stare super antiquas vias, hold one's own, hold one's ground, stand one's ground, embalm, cure, salt, pickle, season, kyanize, bottle, pot, tin, can, sterilize, pasteurize, radiate, dry, lyophilize, freeze- dry, concentrate, evaporate, freeze, quick-freeze, deep-freeze, husband.

N  defense, protection, guard, ward, shielding, propugnation, preservation, guardianship, area defense, site defense, self-defense, self-preservation, resistance, safeguard, balistraria, bunker, screen, camouflage, fortification, munition, muniment, trench, foxhole, bulwark, fosse, moat, ditch, entrenchment, intrenchment, kila, dike, dyke, parapet, sunk fence, embankment, mound, mole, bank, sandbag, revetment, earth work, field- work, fence, wall dead wall, contravallation, paling, palisade, haha, stockade, stoccado, laager, sangar, barrier, barricade, boom, portcullis, chevaux de frise, abatis, abattis, abbatis, vallum, circumvallation, battlement, rampart, scarp, escarp, counter-scarp, glacis, casemate, vallation, vanfos, buttress, abutment, shore, breastwork, banquette, curtain, mantlet, bastion, redan, ravelin, vauntmure, advance work, horn work, outwork, barbacan, barbican, redoubt, fort-elage, fort-alice, lines, loophole, machicolation, sally port, hold, stronghold, fastness, asylum, keep, donjon, dungeon, fortress, citadel, capitol, castle, tower of strength, tower of strength, fort, barracoon, pah, sconce, martello tower, peelhouse, blockhouse, rath, wooden walls, bulletproof vest, armored vest, buffer, corner stone, fender, apron, mask, gauntlet, thimble, carapace, armor, shield, buckler, aegis, breastplate, backplate, cowcatcher, face guard, scutum, cuirass, habergeon, mail, coat of mail, brigandine, hauberk, lorication, helmet, helm, bassinet, salade, heaume, morion, murrion, armet, cabaset, vizor, casquetel, siege cap, headpiece, casque, pickelhaube, vambrace, shako, bearskin, panoply, truncheon, garrison, picket, piquet, defender, protector, guardian, bodyguard, champion, knight-errant, Paladin, propugner, bulletproof window, hardened site, defending, defensive, mural, armed, armed at all points, armed cap-a-pie, armed to the teeth, panoplied, iron-plated, ironclad, loopholed, castellated, machicolated, casemated, defended, proof against, armored, ballproof, bulletproof, hardened, defensively, on the defense, on the defensive, in defense, at bay, pro aris et focis, Int, no surrender!, defense not defiance, Dieu defend le droit, fidei defensor, defender of the faith.

VB  defend, forfend, fend, shield, screen, shroud, engarrison, fend round, fence, entrench, intrench, guard, guard against, take care of, bear harmless, fend off, keep off, ward off, beat off, beat back, hinder, parry, repel, propugn, put to flight, give a warm reception to, hold at bay, keep at bay, keep arm's length, stand on the defensive, act on the defensive, show fight, maintain one's ground, stand one's ground, stand by, hold one's own, bear the brunt, stand the brunt, fall back upon, hold, stand in the gap.

N  combatant, disputant, controversialist, polemic, litigant, belligerent, competitor, rival, corrival, fighter, assailant, champion, Paladin, mosstrooper, swashbuckler fire eater, duelist, bully, bludgeon man, rough, prize fighter, pugilist, boxer, bruiser, the fancy, gladiator, athlete, wrestler, fighting-cock, game-cock, warrior, soldier, fighting man, Amazon, man at arms, armigerent, campaigner, veteran, swordsman, sabreur, redcoat, military man, Rajput, armed force, troops, soldiery, military forces, sabaoth, the army, standing army, regulars, the line, troops of the line, militia, yeomanry, volunteers, trainband, fencible, auxiliary, bersagliere, brave, garde-nationale, garde-royale, minuteman, auxiliary forces, reserve forces, reserves, posse comitatus, national guard, gendarme, beefeater, guards, guardsman, yeomen of the guard, life guards, household troops, janissary, myrmidon, Mama, Mameluke, spahee, spahi, Cossack, Croat, Pandoz, irregular, guerilla, partisan, condottiere, franctireur, tirailleur, bashi-bazouk, vietminh, vietcong, shining path, contras, huk, hukbalahap, mercenary, soldier of fortune, hired gun, gunfighter, gunslinger, bushwhacker, free lance, companion, Hessian, hit man torpedo, soldier, levy, draught, Landwehr, Landsturm, conscript, recruit, cadet, raw levies, infantry, infantryman, private, private soldier, foot soldier, Tommy Atkins, rank and file, peon, trooper, sepoy, legionnaire, legionary, cannon fodder, food for powder, officer, subaltern, ensign, standard bearer, spearman, pikeman, spear bearer, halberdier, lancer, musketeer, carabineer, rifleman, jager, sharpshooter, yager, skirmisher, grenadier, fusileer, archer, bowman, horse and foot, horse soldier, cavalry, horse, artillery, horse artillery, light horse, voltigeur, uhlan, mounted rifles, dragoon, hussar, light dragoon, heavy dragoon, heavy, cuirassier, Foot Guards, Horse Guards, gunner, cannoneer, bombardier, artilleryman, matross, sapper, sapper and miner, engineer, light infantry, rifles, chasseur, zouave, military train, coolie, army, corps d'armee, host, division, battalia, column, wing, detachment, garrison, flying column, brigade, regiment, corps, battalion, sotnia, squadron, company, platoon, battery, subdivision, section, squad, piquet, picket, guard, rank, file, legion, phalanx, cohort, cloud of skirmishers, war horse, charger, destrier, marine, man-of-war's man, navy, wooden walls, naval forces, fleet, flotilla, armada, squadron, man-of-war, destroyer, submarine, minesweeper, torpedo-boat, torpedo-destroyer, patrol torpedo boat, PT boat, torpedo- catcher, war castle, H, M, S, battleship, battle wagon, dreadnought, line of battle ship, ship of the line, aircraft carrier, carrier, flattop, helicopter carrier, missile platform, missile boat, ironclad, turret ship, ram, monitor, floating battery, first- rate, frigate, sloop of war, corvette, gunboat, bomb vessel, flagship, guard ship, cruiser, armored cruiser, protected cruiser, privateer, tender, store ship, troop ship, transport, catamaran, merchant marine.

N  keeper, custodian, custos, ranger, warder, jailer, gaoler, turnkey, castellan, guard, watchdog, watchman, Charley, chokidar, durwan, hayward, sentry, sentinel, watch and ward, concierge, coast guard, guarda costa, game keeper, escort, bodyguard, protector, governor, duenna, guardian, governess, nurse, nanny, babysitter, catsitter, dogsitter, bonne, ayah.

N  traveler, wayfarer, voyager, itinerant, passenger, commuter, tourist, excursionist, explorer, adventurer, mountaineer, hiker, backpacker, Alpine Club, peregrinator, wanderer, rover, straggler, rambler, bird of passage, gadabout, gadling, vagrant, scatterling, landloper, waifs and estrays, wastrel, foundling, loafer, tramp, tramper, vagabond, nomad, Bohemian, gypsy, Arab, Wandering Jew, Hadji, pilgrim, palmer, peripatetic, somnambulist, emigrant, fugitive, refugee, beach comber, booly, globegirdler, globetrotter, vagrant, hobo, night walker, sleep walker, noctambulist, runabout, straphanger, swagman, swagsman, trecker, trekker, zingano, zingaro, runner, courier, Mercury, Iris, Ariel, comet, pedestrian, walker, foot passenger, cyclist, wheelman, rider, horseman, equestrian, cavalier, jockey, roughrider, trainer, breaker, driver, coachman, whip, Jehu, charioteer, postilion, postboy, carter, wagoner, drayman, cabman, cabdriver, voiturier, vetturino, condottiere, engine driver, stoker, fireman, guard, chauffeur, conductor, engineer, gharry-wallah, gari-wala, hackman, syce, truckman, on the road.

advance guard, air national guard, arm guard, army national guard, axle guard, bank guard, body guard, bumper guard, cattle guard, coast guard, color guard, crossing guard, door guard, face guard, guard against, guard boat, guard dog, guard duty, guard hair, guard of honor, guard ship, home guard, honor guard, keep guard, national guard, national guard bureau, off guard, off her guard, off his guard, off one's guard, off your guard, old guard, on guard, on one's guard, on your guard, praetorian guard, prison guard, provost guard, red guard, republican guard, security guard, shin guard, splash guard, stand guard, u. s. coast guard, united states coast guard, upon one's guard, us coast guard, watch guard, yeoman of the guard