1.  To part with unintentionally or unwillingly, as by accident, misfortune, negligence, penalty, forfeit, etc.; to be deprived of; as, to lose money from one's purse or pocket, or in business or gaming; to lose an arm or a leg by amputation; to lose men in battle. [1913 Webster]
"Fair Venus wept the sad disaster
Of having lost her favorite dove." [1913 Webster]

2.  To cease to have; to possess no longer; to suffer diminution of; as, to lose one's relish for anything; to lose one's health. [1913 Webster]
"If the salt hath lost his savor, wherewith shall it be salted?" [1913 Webster]

3.  Not to employ; to employ ineffectually; to throw away; to waste; to squander; as, to lose a day; to lose the benefits of instruction. [1913 Webster]
"The unhappy have but hours, and these they lose." [1913 Webster]

4.  To wander from; to miss, so as not to be able to and; to go astray from; as, to lose one's way. [1913 Webster]
"He hath lost his fellows." [1913 Webster]

5.  To ruin; to destroy; as destroy; as, the ship was lost on the ledge. [1913 Webster]
"The woman that deliberates is lost." [1913 Webster]

6.  To be deprived of the view of; to cease to see or know the whereabouts of; as, he lost his companion in the crowd. [1913 Webster]
"Like following life thro' creatures you dissect,
You lose it in the moment you detect." [1913 Webster]

7.  To fail to obtain or enjoy; to fail to gain or win; hence, to fail to catch with the mind or senses; to miss; as, I lost a part of what he said. [1913 Webster]
"He shall in no wise lose his reward." [1913 Webster]
"I fought the battle bravely which I lost,
And lost it but to Macedonians." [1913 Webster]

8.  To cause to part with; to deprive of. [1913 Webster]
"How should you go about to lose him a wife he loves with so much passion?" [1913 Webster]

9.  To prevent from gaining or obtaining. [1913 Webster]
"O false heart! thou hadst almost betrayed me to eternal flames, and lost me this glory." [1913 Webster]
"In the excitement of such a discovery, many scholars lost their heads."

   To suffer loss, disadvantage, or defeat; to be worse off, esp. as the result of any kind of contest. [1913 Webster]
"We 'll . . . hear poor rogues
Talk of court news; and we'll talk with them too,
Who loses and who wins; who's in, who's out." [1913 Webster]

lose, v. (past and past part. lost)
1 tr. be deprived of or cease to have, esp. by negligence or misadventure.
2 tr. a be deprived of (a person, esp. a close relative) by death. b suffer the loss of (a baby) in childbirth.
3 tr. become unable to find; fail to keep in sight or follow or mentally grasp (lose one's way).
4 tr. let or have pass from one's control or reach (lose one's chance; lose one's bearings).
5 tr. be defeated in (a game, race, lawsuit, battle, etc.).
6 tr. evade; get rid of (lost our pursuers).
7 tr. fail to obtain, catch, or perceive (lose a train; lose a word).
8 tr. forfeit (a stake, deposit, right to a thing, etc.).
9 tr. spend (time, efforts, etc.) to no purpose (lost no time in raising the alarm).
10 intr. a suffer loss or detriment; incur a disadvantage. b be worse off, esp. financially.
11 tr. cause (a person) the loss of (will lose you your job).
12 intr. & tr. (of a timepiece) become slow; become slow by (a specified amount of time).
13 tr. (in passive) disappear, perish; be dead (was lost in the war; is a lost art).

Idiom:
be lost (or lose oneself) in be engrossed in. be lost on be wasted on, or not noticed or appreciated by. be lost to be no longer affected by or accessible to (is lost to pity; is lost to the world). be lost without have great difficulty if deprived of (am lost without my diary). get lost sl. (usu. in imper.) go away. lose one's balance
1 fail to remain stable; fall.
2 fail to retain one's composure. lose one's cool colloq. lose one's composure. lose face be humiliated; lose one's credibility. lose ground see GROUND(1). lose one's head see HEAD. lose heart be discouraged. lose one's heart see HEART. lose one's nerve become timid or irresolute. lose out (often foll. by on) colloq. be unsuccessful; not get a fair chance or advantage (in). lose one's temper become angry. lose time allow time to pass with something unachieved etc. lose touch see TOUCH. lose track of see TRACK(1). lose the (or one's) way become lost; fail to reach one's destination. losing battle a contest or effort in which failure seems certain.
lost cause
1 an enterprise etc. with no chance of success.
2 a person one can no longer hope to influence.
lost generation
1 a generation with many of its men killed in war, esp. that of 1914-18.
2 an emotionally and culturally unstable generation coming to maturity, esp. in 1915-25.

Derivative:
losable adj.

Etymology:
OE losian perish, destroy f. los loss

VB  fail, be unsuccessful, not succeed, make vain efforts, do in vain, labor in vain, toil in vain, flunk, lose one's labor, take nothing by one's motion, bring to naught, make nothing of, wash a blackamoor white, roll the stones of Sisyphus, do by halves, lose ground, fall short of, miss, miss one's aim, miss the mark, miss one's footing, miss stays, slip, trip, stumble, make a slip, blunder, make a mess of, make a botch of, bitch it, miscarry, abort, go up like a rocket and come down like the stick, come down in flames, get shot down, reckon without one's host, get the wrong pig by the tail, get the wrong sow by the ear, limp, halt, hobble, titubate, fall, tumble, lose one's balance, fall to the ground, fall between two stools, flounder, falter, stick in the mud, run aground, split upon a rock, beat one's head against a stone wall, run one's head against a stone wall, knock one's head against a stone wall, dash one's head against a stone wall, break one's back, break down, sink, drown, founder, have the ground cut from under one, get into trouble, get into a mess, get into a scrape, come to grief, go to the wall, go to the dogs, go to pot, lick the dust, bite the dust, be defeated, have the worst of it, lose the day, come off second best, lose, fall a prey to, succumb, not have a leg to stand on, come to nothing, end in smoke, flat out, fall to the ground, fall through, fall dead, fall stillborn, fall flat, slip through one's fingers, hang fire, miss fire, flash in the pan, collapse, topple down, go to wrack and ruin, go amiss, go wrong, go cross, go hard with, go on a wrong tack, go on ill, come off ill, turn out ill, work ill, take a wrong term, take an ugly term, take an ugly turn, take a turn for the worse, be all over with, be all up with, explode, dash one's hopes, defeat the purpose, sow the wind and reap the whirlwind, jump out of the frying pan into the fire, go from the frying pan into the fire.

VB  lose, incur a loss, experience a loss, meet with a loss, miss, mislay, let slip, allow to slip through the fingers, be without, forfeit, get rid of, waste, be lost, lapse.

VB  forget, be forgetful, fall into oblivion, sink into oblivion, have a short memory, have no head, forget one's own name, have on the tip of one's tongue, come in one ear and go out the other, slip memory, escape memory, fade from memory, die away from the memory, lose, lose sight of, fail to recall, not be able to recall, unlearn, efface, discharge from the memory, consign to oblivion, consign to the tomb of the Capulets, think no more of, cast behind one's back, wean one's thoughts from, let bygones be bygones.

VB  be unintelligible, require explanation, have a doubtful meaning, pass comprehension, render unintelligible, conceal, darken, confuse, perplex, not understand, lose, lose the clue, miss, not know what to make of, be able to make nothing of, give it up, not be able to account for, not be able to make either head or tail of, be at sea, wonder, see through a glass darkly, not understand one another, play at cross purposes.

lose ground, lose heart, lose it, lose one's temper, lose sight of, lose weight