The Collaborative International Dictionary of English v.0.48:

Gain \Gain\, v. t. [imp. & p. p. Gained (g[=a]nd); p. pr. &
   vb. n. Gaining.] [From gain, n. but. prob. influenced by F.
   gagner to earn, gain, OF. gaaignier to cultivate, OHG.
   weidin[=o]n, weidinen to pasture, hunt, fr. weida pasturage,
   G. weide, akin to Icel. vei[eth]r hunting, AS. w[=a][eth]u,
   cf. L. venari to hunt, E. venison. See Gain, n., profit.]
   [1913 Webster]
   1. To get, as profit or advantage; to obtain or acquire by
      effort or labor; as, to gain a good living.
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            What is a man profited, if he shall gain the whole
            world, and lose his own soul?         --Matt. xvi.
                                                  26.
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            To gain dominion, or to keep it gained. --Milton.
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            For fame with toil we gain, but lose with ease.
                                                  --Pope.
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   2. To come off winner or victor in; to be successful in; to
      obtain by competition; as, to gain a battle; to gain a
      case at law; to gain a prize.
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   3. To draw into any interest or party; to win to one's side;
      to conciliate.
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            If he shall hear thee, thou hast gained thy brother.
                                                  --Matt. xviii.
                                                  15.
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            To gratify the queen, and gained the court.
                                                  --Dryden.
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   4. To reach; to attain to; to arrive at; as, to gain the top
      of a mountain; to gain a good harbor.
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            Forded Usk and gained the wood.       --Tennyson.
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   5. To get, incur, or receive, as loss, harm, or damage. [Obs.
      or Ironical]
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            Ye should . . . not have loosed from Crete, and to
            have gained this harm and loss.       --Acts xxvii.
                                                  21.
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   Gained day, the calendar day gained in sailing eastward
      around the earth.

   To gain ground, to make progress; to advance in any
      undertaking; to prevail; to acquire strength or extent.

   To gain over, to draw to one's party or interest; to win
      over.

   To gain the wind (Naut.), to reach the windward side of
      another ship.

   Syn: To obtain; acquire; get; procure; win; earn; attain;
        achieve.

   Usage: See Obtain. -- To Gain, Win. Gain implies only
          that we get something by exertion; win, that we do it
          in competition with others. A person gains knowledge,
          or gains a prize, simply by striving for it; he wins a
          victory, or wins a prize, by taking it in a struggle
          with others.
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The Collaborative International Dictionary of English v.0.48:

Gain \Gain\, n. [Cf. W. gan a mortise.] (Arch.)
   A square or beveled notch cut out of a girder, binding joist,
   or other timber which supports a floor beam, so as to receive
   the end of the floor beam.
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The Collaborative International Dictionary of English v.0.48:

Gain \Gain\, a. [OE. gein, gain, good, near, quick; cf. Icel.
   gegn ready, serviceable, and gegn, adv., against, opposite.
   Cf. Ahain.]
   Convenient; suitable; direct; near; handy; dexterous; easy;
   profitable; cheap; respectable. [Obs. or Prov. Eng.]
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The Collaborative International Dictionary of English v.0.48:

Gain \Gain\ (g[=a]n), n. [OE. gain, gein, ga[yogh]hen, gain,
   advantage, Icel. gagn; akin to Sw. gagn, Dan. gavn, cf. Goth.
   gageigan to gain. The word was prob. influenced by F. gain
   gain, OF. gaain. Cf. Gain, v. t.]
   1. That which is gained, obtained, or acquired, as increase,
      profit, advantage, or benefit; -- opposed to loss.
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            But what things were gain to me, those I counted
            loss for Christ.                      --Phil. iii.
                                                  7.
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            Godliness with contentment is great gain. --1 Tim.
                                                  vi. 6.
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            Every one shall share in the gains.   --Shak.
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   2. The obtaining or amassing of profit or valuable
      possessions; acquisition; accumulation. "The lust of
      gain." --Tennyson.
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The Collaborative International Dictionary of English v.0.48:

Gain \Gain\, v. i.
   To have or receive advantage or profit; to acquire gain; to
   grow rich; to advance in interest, health, or happiness; to
   make progress; as, the sick man gains daily.
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         Thou hast greedily gained of thy neighbors by
         extortion.                               --Ezek. xxii.
                                                  12.
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   Gaining twist, in rifled firearms, a twist of the grooves,
      which increases regularly from the breech to the muzzle.

   To gain on or To gain upon.
   (a) To encroach on; as, the ocean gains on the land.
   (b) To obtain influence with.
   (c) To win ground upon; to move faster than, as in a race or
       contest.
   (d) To get the better of; to have the advantage of.
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             The English have not only gained upon the Venetians
             in the Levant, but have their cloth in Venice
             itself.                              --Addison.
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             My good behavior had so far gained on the emperor,
             that I began to conceive hopes of liberty. --Swift.
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WordNet (r) 3.0 (2006):

gain
    n 1: a quantity that is added; "there was an addition to
         property taxes this year"; "they recorded the cattle's gain
         in weight over a period of weeks" [syn: addition,
         increase, gain]
    2: the advantageous quality of being beneficial [syn: profit,
       gain]
    3: the amount of increase in signal power or voltage or current
       expressed as the ratio of output to input [syn:
       amplification, gain]
    4: the amount by which the revenue of a business exceeds its
       cost of operating [ant: loss, red, red ink]
    v 1: obtain; "derive pleasure from one's garden" [syn: derive,
         gain]
    2: win something through one's efforts; "I acquired a passing
       knowledge of Chinese"; "Gain an understanding of
       international finance" [syn: acquire, win, gain] [ant:
       lose]
    3: derive a benefit from; "She profited from his vast
       experience" [syn: profit, gain, benefit]
    4: reach a destination, either real or abstract; "We hit Detroit
       by noon"; "The water reached the doorstep"; "We barely made
       it to the finish line"; "I have to hit the MAC machine before
       the weekend starts" [syn: reach, make, attain, hit,
       arrive at, gain]
    5: obtain advantages, such as points, etc.; "The home team was
       gaining ground"; "After defeating the Knicks, the Blazers
       pulled ahead of the Lakers in the battle for the number-one
       playoff berth in the Western Conference" [syn: gain,
       advance, win, pull ahead, make headway, get ahead,
       gain ground] [ant: drop off, fall back, fall behind,
       lose, recede]
    6: rise in rate or price; "The stock market gained 24 points
       today" [syn: advance, gain]
    7: increase or develop; "the peace movement gained momentum";
       "the car gathers speed" [syn: gain, gather]
    8: earn on some commercial or business transaction; earn as
       salary or wages; "How much do you make a month in your new
       job?"; "She earns a lot in her new job"; "this merger brought
       in lots of money"; "He clears $5,000 each month" [syn:
       gain, take in, clear, make, earn, realize,
       realise, pull in, bring in]
    9: increase (one's body weight); "She gained 20 pounds when she
       stopped exercising" [syn: gain, put on] [ant: lose
       weight, melt off, reduce, slenderize, slim, slim
       down, thin]