The Collaborative International Dictionary of English v.0.48:

Forfeit \For"feit\, n. [OE. forfet crime, penalty, F. forfait
   crime (LL. forefactum, forifactum), prop. p. p. of forfaire
   to forfeit, transgress, fr. LL. forifacere, prop., to act
   beyond; L. foris out of doors, abroad, beyond + facere to do.
   See Foreign, and Fact.]
   1. Injury; wrong; mischief. [Obs. & R.]
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            To seek arms upon people and country that never did
            us any forfeit.                       --Ld. Berners.
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   2. A thing forfeit or forfeited; what is or may be taken from
      one in requital of a misdeed committed; that which is
      lost, or the right to which is alienated, by a crime,
      offense, neglect of duty, or breach of contract; hence, a
      fine; a mulct; a penalty; as, he who murders pays the
      forfeit of his life.
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            Thy slanders I forgive; and therewithal
            Remit thy other forfeits.             --Shak.
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   3. Something deposited and redeemable by a sportive fine; --
      whence the game of forfeits.
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            Country dances and forfeits shortened the rest of
            the day.                              --Goldsmith.
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The Collaborative International Dictionary of English v.0.48:

Forfeit \For"feit\, v. i.
   1. To be guilty of a misdeed; to be criminal; to transgress.
      [Obs.]
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   2. To fail to keep an obligation. [Obs.]
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            I will have the heart of him if he forfeit. --Shak.
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The Collaborative International Dictionary of English v.0.48:

Forfeit \For"feit\, p. p. or a.
   In the condition of being forfeited; subject to alienation.
   --Shak.
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         Once more I will renew
         His laps[`e]d powers, though forfeite.   --Milton.
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The Collaborative International Dictionary of English v.0.48:

Forfeit \For"feit\, a. [F. forfait, p. p. of forfaire. See
   Forfeit, n.]
   Lost or alienated for an offense or crime; liable to penal
   seizure.
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         Thy wealth being forfeit to the state.   --Shak.
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         To tread the forfeit paradise.           --Emerson.
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The Collaborative International Dictionary of English v.0.48:

Forfeit \For"feit\, v. t. [imp. & p. p. Forfeited; p. pr. &
   vb. n. Forfeiting.] [OE. forfeten. See Forfeit, n.]
   To lose, or lose the right to, by some error, fault, offense,
   or crime; to render one's self by misdeed liable to be
   deprived of; to alienate the right to possess, by some
   neglect or crime; as, to forfeit an estate by treason; to
   forfeit reputation by a breach of promise; -- with to before
   the one acquiring what is forfeited.
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         [They] had forfeited their property by their crimes.
                                                  --Burke.
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         Undone and forfeited to cares forever!   --Shak.
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WordNet (r) 3.0 (2006):

forfeit
    adj 1: surrendered as a penalty [syn: confiscate, forfeit,
           forfeited]
    n 1: something that is lost or surrendered as a penalty; [syn:
         forfeit, forfeiture]
    2: a penalty for a fault or mistake that involves losing or
       giving up something; "the contract specified forfeits if the
       work was not completed on time" [syn: forfeit,
       forfeiture]
    3: the act of losing or surrendering something as a penalty for
       a mistake or fault or failure to perform etc. [syn:
       forfeit, forfeiture, sacrifice]
    v 1: lose (s.th.) or lose the right to (s.th.) by some error,
         offense, or crime; "you've forfeited your right to name
         your successor"; "forfeited property" [syn: forfeit,
         give up, throw overboard, waive, forgo, forego]
         [ant: arrogate, claim, lay claim]

Moby Thesaurus II by Grady Ward, 1.0:

78 Moby Thesaurus words for "forfeit":
   amercement, be bereaved of, bereavement, caution, caution money,
   charge, collateral, collateral security, cost, damage, damages,
   dead loss, debit, default, denial, denudation, deposit,
   deprivation, despoilment, destruction, detriment, dispossession,
   distraint, distress, divestment, drop, escheat, escheatment,
   expense, fee, fine, forfeiture, forgo, forgone, give over, give up,
   go astray from, incur loss, injury, kiss good-bye, let slip, lose,
   lose out, loser, losing, losing streak, loss, lost, margin, mislay,
   misplace, miss, mulct, penalty, perdition, privation, relinquish,
   relinquished, renounce, renounced, robbery, ruin, sacrifice,
   sconce, sequestration, spoliation, stake, stripping, suffer loss,
   surrender, surrendered, taking away, total loss, undergo privation,
   waive, waived, wander from, yielded