1.  A collection of visible vapor, or watery particles, suspended in the upper atmosphere. [1913 Webster]
" A classification of clouds according to their chief forms was first proposed by the meteorologist Howard, and this is still substantially employed. The following varieties and subvarieties are recognized: (a) Cirrus. This is the most elevated of all the forms of clouds; is thin, long-drawn, sometimes looking like carded wool or hair, sometimes like a brush or room, sometimes in curl-like or fleecelike patches. It is the cat's-tail of the sailor, and the mare's-tail of the landsman. (b) Cumulus. This form appears in large masses of a hemispherical form, or nearly so, above, but flat below, one often piled above another, forming great clouds, common in the summer, and presenting the appearance of gigantic mountains crowned with snow. It often affords rain and thunder gusts. (c) Stratus. This form appears in layers or bands extending horizontally. (d) Nimbus. This form is characterized by its uniform gray tint and ragged edges; it covers the sky in seasons of continued rain, as in easterly storms, and is the proper rain cloud. The name is sometimes used to denote a raining cumulus, or cumulostratus. (e) Cirro-cumulus. This form consists, like the cirrus, of thin, broken, fleecelice clouds, but the parts are more or less rounded and regulary grouped. It is popularly called mackerel sky. (f) Cirro-stratus. In this form the patches of cirrus coalesce in long strata, between cirrus and stratus. (g) Cumulo-stratus. A form between cumulus and stratus, often assuming at the horizon a black or bluish tint. -- Fog, cloud, motionless, or nearly so, lying near or in contact with the earth's surface. -- Storm scud, cloud lying quite low, without form, and driven rapidly with the wind." [1913 Webster]
"I do set my bow in the cloud." [1913 Webster]

2.  A mass or volume of smoke, or flying dust, resembling vapor. Ezek. viii. 11. [1913 Webster]

3.  A dark vein or spot on a lighter material, as in marble; hence, a blemish or defect; as, a cloud upon one's reputation; a cloud on a title. [1913 Webster]

4.  That which has a dark, lowering, or threatening aspect; that which temporarily overshadows, obscures, or depresses; as, a cloud of sorrow; a cloud of war; a cloud upon the intellect. [1913 Webster]

5.  A great crowd or multitude; a vast collection. Heb. xii. 1. [1913 Webster]

6.  A large, loosely-knitted scarf, worn by women about the head. [1913 Webster]

1.  To overspread or hide with a cloud or clouds; as, the sky is clouded. [1913 Webster]

2.  To darken or obscure, as if by hiding or enveloping with a cloud; hence, to render gloomy or sullen. [1913 Webster]
"One day too late, I fear me, noble lord,
Hath clouded all thy happy days on earth." [1913 Webster]
"Be not disheartened, then, nor cloud those looks." [1913 Webster]
"Nothing clouds men's minds and impairs their honesty like prejudice." [1913 Webster]

3.  To blacken; to sully; to stain; to tarnish; to damage; -- esp. used of reputation or character. [1913 Webster]
"I would not be a stander-by to hear
My sovereign mistress clouded so, without
My present vengeance taken." [1913 Webster]

4.  To mark with, or darken in, veins or sports; to variegate with colors; as, to cloud yarn. [1913 Webster]
"And the nice conduct of a clouded cane." [1913 Webster]

   To grow cloudy; to become obscure with clouds; -- often used with up. [1913 Webster]
"Worthies, away! The scene begins to cloud." [1913 Webster]

cloud, n. & v.
--n.
1 a visible mass of condensed watery vapour floating in the atmosphere high above the general level of the ground.
2 a mass of smoke or dust.
3 (foll. by of) a great number of insects, birds, etc., moving together.
4 a a state of gloom, trouble, or suspicion. b a frowning or depressed look (a cloud on his brow).
5 a local dimness or a vague patch of colour in or on a liquid or a transparent body.
6 an unsubstantial or fleeting thing.
7 obscurity.
--v.
1 tr. cover or darken with clouds or gloom or trouble.
2 intr. (often foll. by over, up) become overcast or gloomy.
3 tr. make unclear.
4 tr. variegate with vague patches of colour.

Idiom:
cloud-castle a daydream. cloud chamber a device containing vapour for tracking the paths of charged particles, X-rays, and gamma rays. clouded leopard a mottled arboreal S. Asian feline, Neofelis nebulosa. cloud-hopping movement of an aircraft from cloud to cloud esp. for concealment. cloud-land a utopia or fairyland. in the clouds
1 unreal, imaginary, mystical.
2 (of a person) abstracted, inattentive. on cloud nine (or seven) colloq. extremely happy. under a cloud out of favour, discredited, under suspicion. with one's head in the clouds day-dreaming, unrealistic.

Derivative:
cloudless adj. cloudlessly adv. cloudlet n.

Etymology:
OE clud mass of rock or earth, prob. rel. to CLOD

N  assemblage, collection, collocation, colligation, compilation, levy, gathering, ingathering, muster, attroupement, team, concourse, conflux, congregation, contesseration, convergence, meeting, levee, reunion, drawing room, at home, conversazione, assembly, congress, convention, conventicle, gemote, conclave, posse, posse comitatus, Noah's ark, miscellany, collectanea, museum, menagerie, museology, crowd, throng, group, flood, rush, deluge, rabble, mob, press, crush, cohue, horde, body, tribe, crew, gang, knot, squad, band, party, swarm, shoal, school, covey, flock, herd, drove, atajo, bunch, drive, force, mulada, remuda, roundup, array, bevy, galaxy, corps, company, troop, troupe, task force, army, regiment, host, populousness, clan, brotherhood, fraternity, sorority, association, volley, shower, storm, cloud, group, cluster, Pleiades, clump, pencil, set, batch, lot, pack, budget, assortment, bunch, parcel, packet, package, bundle, fascine, fasces, bale, seron, seroon, fagot, wisp, truss, tuft, shock, rick, fardel, stack, sheaf, haycock, fascicle, fascicule, fasciculus, gavel, hattock, stook, accumulation, congeries, heap, lump, pile, rouleau, tissue, mass, pyramid, bing, drift, snowball, snowdrift, acervation, cumulation, glomeration, agglomeration, conglobation, conglomeration, conglomerate, coacervate, coacervation, coagmentation, aggregation, concentration, congestion, omnium gaterum, spicilegium, black hole of Calcutta, quantity, collector, gatherer, whip, whipper in, assembled, closely packed, dense, serried, crowded to suffocation, teeming, swarming, populous, as thick as hops, all of a heap, fasciculated cumulative, the plot thickens, acervatim, tibi seris tibi metis.

N  adversity, evil, failure, bad luck, ill luck, evil luck, adverse luck, hard fortune, hard hap, hard luck, hard lot, frowns of fortune, evil dispensation, evil star, evil genius, vicissitudes of life, ups and downs of life, broken fortunes, hard case, hard lines, hard life, sea of troubles, peck of troubles, hell upon earth, slough of despond, trouble, hardship, curse, blight, blast, load, pressure, pressure of the times, iron age, evil day, time out of joint, hard times, bad times, sad times, rainy day, cloud, dark cloud, gathering clouds, ill wind, visitation, infliction, affliction, bitter pill, care, trial, the sport of fortune, mishap, mischance, misadventure, misfortune, disaster, calamity, catastrophe, accident, casualty, cross, reverse, check, contretemps, rub, backset, comedown, setback, losing game, falling, fall, downfall, ruination, ruinousness, undoing, extremity, ruin, unfortunate, unblest, unhappy, unlucky, improsperous, unprosperous, hoodooed, luckless, hapless, out of luck, in trouble, in a bad way, in an evil plight, under a cloud, clouded, ill off, badly off, in adverse circumstances, poor, behindhand, down in the world, decayed, undone, on the road to ruin, on its last legs, on the wane, in one's utmost need, planet-struck, devoted, born under an evil star, born with a wooden ladle in one's mouth, ill-fated, ill-starred, ill-omened, adverse, untoward, disastrous, calamitous, ruinous, dire, deplorable.

N  multitude, numerous, numerosity, numerality, multiplicity, profusion, legion, host, great number, large number, round number, enormous number, a quantity, numbers, array, sight, army, sea, galaxy, scores, peck, bushel, shoal, swarm, draught, bevy, cloud, flock, herd, drove, flight, covey, hive, brood, litter, farrow, fry, nest, crowd, lots, all in the world and his wife, greater number, majority, multiplication, multiple, many, several, sundry, divers, various, not a few, Briarean, a hundred, a thousand, a myriad, a million, a quadrillion, a nonillion, a thousand and one, some ten or a dozen, some forty or fifty, half a dozen, half a hundred, very many, full many, ever so many, numerous, numerose, profuse, in profusion, manifold, multiplied, multitudinous, multiple, multinominal, teeming, populous, peopled, crowded, thick, studded, galore, thick coming, many more, more than one can tell, a world of, no end of, no end to, cum multis aliis, thick as hops, thick as hail, plenty as blackberries, numerous as the stars in the firmament, numerous as the sands on the seashore, numerous as the hairs on the head, and what not, and heaven knows what, endless, their name is 'legion', acervatim, en foule, many- headed multitude, numerous as glittering gems of morning dew, vel prece vel pretio.

N  gaseity, vaporousness, flatulence, flatulency, volatility, aeration, aerification, elastic fluid, gas, air, vapor, ether, steam, essence, fume, reek, effluvium, flatus, cloud, ammonia, ammoniacal gas, volatile alkali, vacuum, partial vacuum, pneumatics, pneumatostatics, aerostatics, aerodynamics, gasmeter, gasometer, air bladder, swimming bladder, sound, (of a fish), gaseous, aeriform, ethereal, aerial, airy, vaporous, volatile, evaporable, flatulent.

N  air, common air, atmospheric air, atmosphere, aerosphere, open air, sky, welkin, blue sky, cloud, weather, climate, rise and fall of the barometer, isobar, aerology, aerometry, aeroscopy, aeroscopy, aerography, meteorology, climatology, pneumatics, eudioscope, baroscope, aeroscope, eudiometer, barometer, aerometer, aneroid, baroscope, weather gauge, weather glass, weather cock, exposure to the air, exposure to the weather, ventilation, aerostation, aeronautics, aeronaut, containing air, flatulent, effervescent, windy, atmospheric, airy, aerial, aeriform, meteorological, weatherwise, in the open air, a la belle etoile, al fresco, sub jove dio.

N  bubble; cloud, bubble, foam, froth, head, spume, lather, suds, spray, surf, yeast, barm, spindrift, cloud, vapor, fog, mist, haze, steam, geyser, scud, messenger, rack, nimbus, cumulus, woolpack, cirrus, stratus, cirrostratus, cumulostratus, cirrocumulus, mackerel sky, mare's tale, dirty sky, curl cloud, frost smoke, thunderhead, nephelognosy, nephograph, nephology, effervescence, fermentation, bubbling, nebula, cloudliness, nebulosity, bubbling, frothy, nappy, effervescent, sparkling, mousseux, frothy, up, cloudy, thunderheaded, vaporous, nebulous, overcast, the lowring element scowls o'er the darkened lands.

N  dimness, darkness, paleness, half light, demi-jour, partial shadow, partial eclipse, shadow of a shade, glimmer, gliming, nebulosity, cloud, eclipse, aurora, dusk, twilight, shades of evening, crepuscule, cockshut time, break of day, daybreak, dawn, moonlight, moonbeam, moonglade, moonshine, starlight, owl's light, candlelight, rushlight, firelight, farthing candle, dim, dull, lackluster, dingy, darkish, shorn of its beams, dark, faint, shadowed forth, glassy, cloudy, misty, blear, muggy, fuliginous, nebulous, nebular, obnubilated, overcast, crepuscular, muddy, lurid, leaden, dun, dirty, looming, pale, confused.

N  shade, awning, parasol, sunshade, umbrella, chick, portiere, screen, curtain, shutter, blind, gauze, veil, chador, mantle, mask, cloud, mist, gathering, of clouds, umbrage, glade, shadow, beach umbrella, folding umbrella, shady, umbrageous, welcome ye shades! ye bowery thickets hail.

N  opacity, opaqueness, film, cloud, opaque, impervious to light, adiaphanous, dim, turbid, thick, muddy, opacous, obfuscated, fuliginous, cloud, hazy, misty, foggy, vaporous, nubiferous, muggy, smoky, fumid, murky, dirty, opacity, opaqueness, film, cloud, opaque, impervious to light, adiaphanous, dim, turbid, thick, muddy, opacous, obfuscated, fuliginous, cloud, hazy, misty, foggy, vaporous, nubiferous, muggy, smoky, fumid, murky, dirty.

N  ambush, camouflage, mimicry, hiding place, secret place, secret drawer, recess, hold, holes and corners, closet, crypt, adytum, abditory, oubliette, ambush, ambuscade, stalking horse, lurking hole, lurking place, secret path, back stairs, retreat, screen, cover, shade, blinker, veil, curtain, blind, cloak, cloud, mask, visor, vizor, disguise, masquerade dress, domino, pitfall, trap, camouflaged, hidden, concealed, aux aguets.

altocumulus cloud, altostratus cloud, be on cloud nine, cirrocumulus cloud, cirrostratus cloud, cirrus cloud, cloud bank, cloud chamber, cloud cover, cloud grass, cloud nine, cloud over, cloud seeder, cloud up, cumulonimbus cloud, cumulus cloud, dark cloud, dust cloud, large magellanic cloud, magellanic cloud, mother-of-pearl cloud, mushroom cloud, mushroom-shaped cloud, nacreous cloud, nimbus cloud, oort cloud, rain cloud, red cloud, saint cloud, small magellanic cloud, st. cloud, storm cloud, stratus cloud, war cloud, wilson cloud chamber