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.
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            Fair Venus wept the sad disaster
            Of having lost her favorite dove.     --Prior.
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   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.
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            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.
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            The unhappy have but hours, and these they lose.
                                                  --Dryden.
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   4. To wander from; to miss, so as not to be able to and; to
      go astray from; as, to lose one's way.
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            He hath lost his fellows.             --Shak
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   5. To ruin; to destroy; as destroy; as, the ship was lost on
      the ledge.
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            The woman that deliberates is lost.   --Addison.
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   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.
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            Like following life thro' creatures you dissect,
            You lose it in the moment you detect. --Pope.
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   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.
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            He shall in no wise lose his reward.  --Matt. x. 42.
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            I fought the battle bravely which I lost,
            And lost it but to Macedonians.       --Dryden.
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   8. To cause to part with; to deprive of. [R.]
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            How should you go about to lose him a wife he loves
            with so much passion?                 --Sir W.
                                                  Temple.
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   9. To prevent from gaining or obtaining.
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            O false heart! thou hadst almost betrayed me to
            eternal flames, and lost me this glory. --Baxter.
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   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.
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   3. Not employed or enjoyed; thrown away; employed
      ineffectually; wasted; squandered; as, a lost day; a lost
      opportunity or benefit.
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   5. Having wandered from, or unable to find, the way;
      bewildered; perplexed; as, a child lost in the woods; a
      stranger lost in London.
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   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.
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   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]