The Collaborative International Dictionary of English v.0.48:

Lose \Lose\ (l[=oo]z), v. t. [imp. & p. p. Lost (l[o^]st; 115)
   p. pr. & vb. n. Losing (l[=oo]z"[i^]ng).] [OE. losien to
   loose, be lost, lose, AS. losian to become loose; akin to OE.
   leosen to lose, p. p. loren, lorn, AS. le['i]san, p. p. loren
   (in comp.), D. verliezen, G. verlieren, Dan. forlise, Sw.
   f["o]rlisa, f["o]rlora, Goth. fraliusan, also to E. loose, a
   & v., L. luere to loose, Gr. ly`ein, Skr. l[=u] to cut.
   [root]127. Cf. Analysis, Palsy, Solve, Forlorn,
   Leasing, Loose, Loss.]
   [1913 Webster]
   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.     --Prior.
      [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?                            --Matt. v. 13.
      [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.
                                                  --Dryden.
      [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.             --Shak
      [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.   --Addison.
      [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. --Pope.
      [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.  --Matt. x. 42.
      [1913 Webster]

            I fought the battle bravely which I lost,
            And lost it but to Macedonians.       --Dryden.
      [1913 Webster]

   8. To cause to part with; to deprive of. [R.]
      [1913 Webster]

            How should you go about to lose him a wife he loves
            with so much passion?                 --Sir W.
                                                  Temple.
      [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. --Baxter.
      [1913 Webster]

   To lose ground, to fall behind; to suffer gradual loss or
      disadvantage.

   To lose heart, to lose courage; to become timid. "The
      mutineers lost heart." --Macaulay.

   To lose one's head, to be thrown off one's balance; to lose
      the use of one's good sense or judgment, through fear,
      anger, or other emotion.
      [1913 Webster]

            In the excitement of such a discovery, many scholars
            lost their heads.                     --Whitney.

   To lose one's self.
      (a) To forget or mistake the bearing of surrounding
          objects; as, to lose one's self in a great city.
      (b) To have the perceptive and rational power temporarily
          suspended; as, we lose ourselves in sleep.

   To lose sight of.
      (a) To cease to see; as, to lose sight of the land.
      (b) To overlook; to forget; to fail to perceive; as, he
          lost sight of the issue.
          [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Lost \Lost\, a. [Prop. p. p. of OE. losien. See Lose, v. t.]
   1. Parted with unwillingly or unintentionally; not to be
      found; missing; as, a lost book or sheep.
      [1913 Webster]

   2. Parted with; no longer held or possessed; as, a lost limb;
      lost honor.
      [1913 Webster]

   3. Not employed or enjoyed; thrown away; employed
      ineffectually; wasted; squandered; as, a lost day; a lost
      opportunity or benefit.
      [1913 Webster]

   5. Having wandered from, or unable to find, the way;
      bewildered; perplexed; as, a child lost in the woods; a
      stranger lost in London.
      [1913 Webster]

   6. Ruined or destroyed, either physically or morally; past
      help or hope; as, a ship lost at sea; a woman lost to
      virtue; a lost soul.
      [1913 Webster]

   7. Hardened beyond sensibility or recovery; alienated;
      insensible; as, lost to shame; lost to all sense of honor.
      [1913 Webster]

   8. Not perceptible to the senses; no longer visible; as, an
      island lost in a fog; a person lost in a crowd.
      [1913 Webster]

   9. Occupied with, or under the influence of, something, so as
      to be insensible of external things; as, to be lost in
      thought.
      [1913 Webster]

   Lost motion (Mach.), the difference between the motion of a
      driver and that of a follower, due to the yielding of
      parts or looseness of joints.
      [1913 Webster]

WordNet (r) 3.0 (2006):

lost
    adj 1: no longer in your possession or control; unable to be
           found or recovered; "a lost child"; "lost friends"; "his
           lost book"; "lost opportunities" [ant: found]
    2: having lost your bearings; confused as to time or place or
       personal identity; "I frequently find myself disoriented when
       I come up out of the subway"; "the anesthetic left her
       completely disoriented" [syn: confused, disoriented,
       lost]
    3: spiritually or physically doomed or destroyed; "lost souls";
       "a lost generation"; "a lost ship"; "the lost platoon" [ant:
       saved]
    4: not gained or won; "a lost battle"; "a lost prize" [ant:
       won]
    5: incapable of being recovered or regained; "his lost honor"
    6: not caught with the senses or the mind; "words lost in the
       din" [syn: lost, missed]
    7: deeply absorbed in thought; "as distant and bemused as a
       professor listening to the prattling of his freshman class";
       "lost in thought"; "a preoccupied frown" [syn: bemused,
       deep in thought(p), lost(p), preoccupied]
    8: perplexed by many conflicting situations or statements;
       filled with bewilderment; "obviously bemused by his
       questions"; "bewildered and confused"; "a cloudy and
       confounded philosopher"; "just a mixed-up kid"; "she felt
       lost on the first day of school" [syn: baffled,
       befuddled, bemused, bewildered, confounded,
       confused, lost, mazed, mixed-up, at sea]
    9: unable to function; without help [syn: helpless, lost]
    n 1: people who are destined to die soon; "the agony of the
         doomed was in his voice" [syn: doomed, lost]

Moby Thesaurus II by Grady Ward, 1.0:

181 Moby Thesaurus words for "lost":
   abandoned, abashed, ablated, abroad, absent, absentminded,
   absorbed, abstracted, accursed, adrift, astray, at sea, away,
   baffled, bemused, bewildered, beyond recall, beyond remedy,
   bothered, buried, by the board, bygone, castle-building, clueless,
   condemned, confounded, confused, consumed, corrupt, cureless,
   cursed, damned, daydreaming, daydreamy, dead, defunct, departed,
   depleted, desperate, destroyed, devastated, discomposed,
   disconcerted, dismayed, disoriented, dissipated, dissolute,
   distracted, distrait, distraught, disturbed, doomed,
   down the drain, dreaming, dreamy, drowsing, ecstatic, elsewhere,
   embarrassed, engrossed, eroded, exhausted, expended, extinct,
   fallen, faraway, forfeit, forfeited, forgotten, frantic, frenzied,
   godless, gone, gone away, gone to waste, graceless, guessing,
   half-awake, helpless, hopeless, immedicable, in a fix, in a maze,
   in a pickle, in a reverie, in a scrape, in a stew, in the clouds,
   incorrigible, incurable, inoperable, irreclaimable, irrecoverable,
   irredeemable, irreformable, irremediable, irreparable,
   irretrievable, irreversible, irrevocable, lacking, late, long-lost,
   lost in thought, lost to, lost to sight, lost to view, mazed,
   meditative, mislaid, misplaced, misremembered, missing, misspent,
   mooning, moonraking, museful, musing, mystified, napping, no more,
   nodding, nonexistent, obliterated, oblivious, obsolete,
   off the track, out of sight, out the window, passed, past,
   past and gone, past hope, past praying for, past recall, pensive,
   perplexed, perturbed, pipe-dreaming, preoccupied, put-out, puzzled,
   rapt, remediless, reprobate, ruined, run to seed, shriftless,
   shrunken, somewhere else, spent, squandered, stargazing, strayed,
   taken up, terminal, transported, turned around, unchaste,
   unconscious, unconverted, undone, unmitigable, unredeemable,
   unredeemed, unregenerate, unrelievable, unsalvable, unsalvageable,
   unwon, upset, used, used up, vanished, wanton, wasted,
   without a clue, woolgathering, worn away, wrapped in thought,
   wrecked



Bouvier's Law Dictionary, Revised 6th Ed (1856):

LOST. What was once possessed and cannot now be found.
     2. When a bond or other deed was lost, formerly the obligee or
plaintiff was compelled to go into equity to seek relief, because there was
no remedy a law, the plaintiff being required to make profert in his
declaration. 1 Chan. c. 7T. But in process of time courts of law dispensed
with profert in such cases, and thereby obtained concurrent jurisdiction
with the courts of chancery, so that now the loss of any paper, other than a
negotiable note, will not prevent the plaintiff from recovering at law as
well as in equity. 3 Atk. 214; 1 Ves. 341; 5 Ves. 235; 6 Ves. 812, 7 Ves.
19; 3 V. & B. 54.
     3. When a negotiable note has been lost, equity will grant relief. In
such case the claimant must tender an indemnity to the debtor, and file a
bill in chancery to compel payment. 7 B. & C. 90; Ryan & Mo. 90; 4 Taunt.
602; 2 Ves. sen. 327; 16 Ves. 430.