The Collaborative International Dictionary of English v.0.48:

Benefit \Ben"e*fit\, n. [OE. benefet, benfeet, bienfet, F.
   bienfait, fr. L. benefactum; bene well (adv. of bonus good) +
   factum, p. p. of facere to do. See Bounty, and Fact.]
   1. An act of kindness; a favor conferred.
      [1913 Webster]

            Bless the Lord, O my soul, and forget not all his
            benefits.                             --Ps. ciii. 2.
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   2. Whatever promotes prosperity and personal happiness, or
      adds value to property; advantage; profit.
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            Men have no right to what is not for their benefit.
                                                  --Burke.
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   3. A theatrical performance, a concert, or the like, the
      proceeds of which do not go to the lessee of the theater
      or to the company, but to some individual actor, or to
      some charitable use.
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   4. Beneficence; liberality. [Obs.] --Webster (1623).
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   5. pl. Natural advantages; endowments; accomplishments. [R.]
      "The benefits of your own country." --Shak.
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   Benefit of clergy. (Law) See under Clergy.
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   Syn: Profit; service; use; avail. See Advantage.
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The Collaborative International Dictionary of English v.0.48:

Benefit \Ben"e*fit\, v. t. [imp. & p. p. Benefited; p. pr. &
   vb. n. Benefitting.]
   To be beneficial to; to do good to; to advantage; to advance
   in health or prosperity; to be useful to; to profit.
   [1913 Webster]

         I will repent of the good, wherewith I said I would
         benefit them.                            --Jer. xviii.
                                                  10.
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The Collaborative International Dictionary of English v.0.48:

Benefit \Ben"e*fit\, v. i.
   To gain advantage; to make improvement; to profit; as, he
   will benefit by the change.
   [1913 Webster]

WordNet (r) 3.0 (2006):

benefit
    n 1: financial assistance in time of need
    2: something that aids or promotes well-being; "for the benefit
       of all" [syn: benefit, welfare]
    3: a performance to raise money for a charitable cause
    v 1: derive a benefit from; "She profited from his vast
         experience" [syn: profit, gain, benefit]
    2: be beneficial for; "This will do you good" [syn: benefit,
       do good]

Moby Thesaurus II by Grady Ward, 1.0:

166 Moby Thesaurus words for "benefit":
   abet, absolute interest, account, act of grace, act of kindness,
   advance, advantage, aid, allowances, ameliorate, answer, assist,
   assistance, avail, bail out, be handy, be of use, be right,
   bear a hand, befit, befitting, befriend, behalf, behoof,
   benediction, benefaction, benefits, benevolence, benignity,
   benison, bestead, better, bill, blessing, boon, break no bones,
   build, claim, comfort, common, confer a benefit,
   contingent interest, contribute to, convenience, courtesy, debut,
   do, do a favor, do a kindness, do good, do no harm, do the trick,
   doctor, ease, easement, entertainment, equitable interest, equity,
   estate, exhibit, exhibition, farewell performance, favor,
   fill the bill, fit, flesh show, forward, further, gain,
   give a boost, give a hand, give a lift, give good returns,
   give help, godsend, good, good deed, good offices, good turn,
   grace, help, holding, improve, interest, kind deed, kind offices,
   kindly act, kindness, labor of love, lend a hand, lend one aid,
   limitation, manna, mercy, ministration, ministry, mitzvah,
   not come amiss, obligation, office, offices, part, pay, pay off,
   percentage, performance, perks, perquisites, point, premiere,
   presentation, presentment, production, proffer aid, profit,
   promote, prosperity, protect, protection, rally, reclaim, redeem,
   relief, relieve, remedy, render a service, render assistance,
   rescue, restore, resuscitate, revive, right, right of entry, sake,
   save, serve, serve the purpose, service, set up, settlement, show,
   stage presentation, stake, strict settlement, succor, suffice,
   suit the occasion, support, swan song, take in tow,
   theatrical performance, therapy, title, trust, tryout, turn, use,
   value, vested interest, welfare, well-being, work, work for,
   world of good, worth, yield a profit



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

BENEFIT. This word is used in the same sense as gain (q. v.) and profits.
(q. v.) 20 Toull. n. 199.