1.  The act of losing; failure; destruction; privation; as, the loss of property; loss of money by gaming; loss of health or reputation. [1913 Webster]
"Assured loss before the match be played." [1913 Webster]

2.  The state of losing or having lost; the privation, defect, misfortune, harm, etc., which ensues from losing. [1913 Webster]
"Though thou repent, yet I have still the loss." [1913 Webster]

3.  That which is lost or from which one has parted; waste; -- opposed to gain or increase; as, the loss of liquor by leakage was considerable. [1913 Webster]

4.  The state of being lost or destroyed; especially, the wreck or foundering of a ship or other vessel. [1913 Webster]

5.  Failure to gain or win; as, loss of a race or battle. [1913 Webster]

6.  Failure to use advantageously; as, loss of time. [1913 Webster]

7.  Killed, wounded, and captured persons, or captured property. [1913 Webster]

8.  Destruction or diminution of value, if brought about in a manner provided for in the insurance contract (as destruction by fire or wreck, damage by water or smoke), or the death or injury of an insured person; also, the sum paid or payable therefor; as, the losses of the company this year amount to a million of dollars. [1913 Webster]

loss, n.
1 the act or an instance of losing; the state of being lost.
2 a person, thing, or amount lost.
3 the detriment or disadvantage resulting from losing (that is no great loss).

Idiom:
at a loss (sold etc.) for less than was paid for it. be at a loss be puzzled or uncertain. be at a loss for words not know what to say. loss adjuster an insurance agent who assesses the amount of compensation arising from a loss. loss-leader an item sold at a loss to attract customers.

Etymology:
ME los, loss prob. back-form. f. lost, past part. of LOSE

N  evil, ill, harm, hurt, mischief, nuisance, machinations of the devil, Pandora's box, ills that flesh is heir to, blow, buffet, stroke, scratch, bruise, wound, gash, mutilation, mortal blow, wound, immedicabile vulnus, damage, loss, disadvantage, prejudice, drawback, disaster, accident, casualty, mishap, bad job, devil to pay, calamity, bale, catastrophe, tragedy, ruin, adversity, mental suffering, demon, (Evil spirit) bane, (cause of evil), badness, (Production of Evil), painfulness, evil doer, outrage, wrong, injury, foul play, bad turn, ill turn, disservice, spoliation, grievance, crying evil, disastrous, bad, awry, out of joint, disadvantageous, amis, wrong, ill, to one's cost, moving accidents by flood and field.

N  waste, consumption, expenditure, exhaustion, dispersion, ebb, leakage, loss, wear and tear, waste, prodigality, misuse, wasting, rubbish, mountain in labor, wasted, at a low ebb, wasteful, penny wise and pound foolish, magno conatu magnas nugas, le jeu ne vaut pas la chandelle, idly busy rolls their world away.

N  deterioration, debasement, wane, ebb, recession, retrogradation, decrease, degeneracy, degeneration, degenerateness, degradation, depravation, depravement, devolution, depravity, demoralization, retrogression, masochism, impairment, inquination, injury, damage, loss, detriment, delaceration, outrage, havoc, inroad, ravage, scath, perversion, prostitution, vitiation, discoloration, oxidation, pollution, defoedation, poisoning, venenation, leaven, contamination, canker, corruption, adulteration, alloy, decline, declension, declination, decadence, decadency, falling off, caducity, decrepitude, decay, dilapidation, ravages of time, wear and tear, corrosion, erosion, moldiness, rottenness, moth and rust, dry rot, blight, marasmus, atrophy, collapse, disorganization, delabrement (destruction), aphid, Aphis, plant louse, puceron, vinefretter, vinegrub, wreck, mere wreck, honeycomb, magni nominis umbra, jade, plug, rackabones, skate, tackey, tacky, have seen better days, deteriorate, degenerate, fall off, wane, ebb, retrograde, decline, droop, go down, go downhill, go from bad to worse, go farther and fare worse, jump out of the frying pan into the fire, run to seed, go to seed, run to waste swale, sweal, lapse, be the worse for, sphacelate: break, break down, spring a leak, crack, start, shrivel, fade, go off, wither, molder, rot, rankle, decay, go bad, go to decay, fall into decay, fall into the sear and yellow leaf, rust, crumble, shake, totter, totter to its fall, perish, die, deteriorate, weaken, put back, set back, taint, infect, contaminate, poison, empoison, envenom, canker, corrupt, exulcerate, pollute, vitiate, inquinate, debase, embase, denaturalize, denature, leaven, deflower, debauch, defile, deprave, degrade, ulcerate, stain, discolor, alloy, adulterate, sophisticate, tamper with, prejudice, pervert, prostitute, demoralize, brutalize, render vicious, embitter, acerbate, exacerbate, aggravate, injure, impair, labefy, damage, harm, hurt, shend, scath, scathe, spoil, mar, despoil, dilapidate, waste, overrun, ravage, pillage, wound, stab, pierce, maim, lame, surbate, cripple, hough, hamstring, hit between wind and water, scotch, mangle, mutilate, disfigure, blemish, deface, warp, blight, rot, corrode, erode, wear away, wear out, gnaw, gnaw at the root of, sap, mine, undermine, shake, sap the foundations of, break up, disorganize, dismantle, dismast, destroy, damnify, do one's worst, knock down, deal a blow to, play havoc with, play sad havoc with, play the mischief with, play the deuce with, play the very devil with, play havoc among, play sad havoc among, play the mischief among, play the deuce among, play the very devil among, decimate, Adj, unimproved &c (improve), deteriorated, altered, altered for the worse, injured, sprung, withering, spoiling, on the wane, on the decline, tabid, degenerate, marescent, worse, the worse for, all the worse for, out of repair, out of tune, imperfect, the worse for wear, battered, weathered, weather-beaten, stale, passe, shaken, dilapidated, frayed, faded, wilted, shabby, secondhand, threadbare, worn, worn to a thread, worn to a shadow, worn to the stump, worn to rags, reduced, reduced to a skeleton, far gone, tacky, decayed, moth-eaten, worm-eaten, mildewed, rusty, moldy, spotted, seedy, time-worn, moss-grown, discolored, effete, wasted, crumbling, moldering, rotten, cankered, blighted, tainted, depraved, decrepid, decrepit, broke, busted, broken, out of commission, hors de combat, out of action, broken down, done, done for, done up, worn out, used up, finished, beyond saving, fit for the dust hole, fit for the wastepaper basket, past work, at a low ebb, in a bad way, on one's last legs, undermined, deciduous, nodding to its fall, tottering, past cure, fatigued, retrograde, deleterious, out of the frying pan into the fire, agrescit medendo, what a falling off was there!.

N  decrement, discount, defect, loss, deduction, afterglow, eduction, waste.

N  loss, deperdition, perdition, forfeiture, lapse, privation, bereavement, deprivation, riddance, damage, squandering, waste, losing, not having, shorn of, deprived of, denuded, bereaved, bereft, minus, cut off, dispossessed, rid of, quit of, out of pocket, lost, long lost, irretrievable, off one's hands, Int, farewell to!, adieu to.

N  death, decease, demise, dissolution, departure, obit, release, rest, quietus, fall, loss, bereavement, mortality, morbidity, end of life &c, cessation of life &c, loss of life, extinction of life, ebb of life, death warrant, death watch, death rattle, death bed, stroke of death, agonies of death, shades of death, valley of death, jaws of death, hand of death, last breath, last gasp, last agonies, dying day, dying breath, dying agonies, chant du cygne, rigor mortis, Stygian shore, King of terrors, King Death, Death, doom, Hell's grim Tyrant, euthanasia, break up of the system, natural death, natural decay, sudden death, violent death, untimely end, watery grave, debt of nature, suffocation, asphyxia, fatal disease, death blow, necrology, bills of mortality, obituary, death song, dead, lifeless, deceased, demised, departed, defunct, extinct, late, gone, no more, exanimate, inanimate, out of the world, taken off, released, departed this life, dead and gone, dead as a doornail, dead as a doorpost, dead as a mutton, dead as a herring, dead as nits, launched into eternity, gone to one's eternal reward, gone to meet one's maker, pushing up daisies, gathered to one's fathers, numbered with the dead, dying, moribund, morient, hippocratic, in articulo, in extremis, in the jaws of death, in the agony of death, going off, aux abois, one one's last legs, on one's death bed, at the point of death, at death's door, at the last gasp, near one's end, given over, booked, with one foot in the grave, tottering on the brink of the grave, stillborn, mortuary, deadly, post obit, post mortem, life ebbs, life fails, life hangs by a thread, one's days are numbered, one's hour is come, one's race is run, one's doom is sealed, Death knocks at the door, Death stares one in the face, the breath is out of the body, the grave closes over one, sic itur ad astra, de mortuis nil nisi bonum, dulce et decorum est pro patria mori, honesta mors turpi vita potior, in adamantine chains shall death be bound, mors ultima linea rerum est, ominia mors aequat, Spake the grisly Terror, the lone couch of this everlasting sleep, nothing is certain but death and taxes.

at a loss, capital loss, conductive hearing loss, core loss, financial loss, hearing loss, loss leader, loss of consciousness, loss ratio, memory loss, paper loss, profit and loss, profit and loss account, sensorineural hearing loss, total loss, turn a loss