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.
      [1913 Webster]

            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.
      [1913 Webster]

            For fame with toil we gain, but lose with ease.
                                                  --Pope.
      [1913 Webster]

   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.
      [1913 Webster]

   3. To draw into any interest or party; to win to one's side;
      to conciliate.
      [1913 Webster]

            If he shall hear thee, thou hast gained thy brother.
                                                  --Matt. xviii.
                                                  15.
      [1913 Webster]

            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.
      [1913 Webster]

            Forded Usk and gained the wood.       --Tennyson.
      [1913 Webster]

   5. To get, incur, or receive, as loss, harm, or damage. [Obs.
      or Ironical]
      [1913 Webster]

            Ye should . . . not have loosed from Crete, and to
            have gained this harm and loss.       --Acts xxvii.
                                                  21.
      [1913 Webster]

   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.
          [1913 Webster]

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.
   [1913 Webster]

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.]
   [1913 Webster]

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.
      [1913 Webster]

            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.
      [1913 Webster]

   2. The obtaining or amassing of profit or valuable
      possessions; acquisition; accumulation. "The lust of
      gain." --Tennyson.
      [1913 Webster]

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.
   [1913 Webster]

         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.
       [1913 Webster]

             The English have not only gained upon the Venetians
             in the Levant, but have their cloth in Venice
             itself.                              --Addison.
       [1913 Webster]

             My good behavior had so far gained on the emperor,
             that I began to conceive hopes of liberty. --Swift.
       [1913 Webster]

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]

Moby Thesaurus II by Grady Ward, 1.0:

348 Moby Thesaurus words for "gain":
   accept, access, accession, accomplish, accretion, accrual, accrue,
   accruement, accumulate, accumulation, achieve, achievement,
   acquire, acquisition, addition, admit, advance, advantage,
   aggrandizement, ameliorate, amend, amplification, appreciate,
   appreciation, approach, argue into, arrive, arrive at, arrive in,
   ascent, assume, attain, attain to, attainment, augmentation, avail,
   available gain, bag, balloon, ballooning, be received,
   be responsible for, be seized of, bear the palm, behalf, behoof,
   benefit, benison, blessing, bloat, bloating, blow in, bob up, boom,
   boon, boost, breed, bring down, bring in, bring on, bring over,
   bring round, bring to reason, bring upon, broaden, broadening,
   buildup, capital gains, captivate, capture, carry, carry away,
   carry it, carry off, carry the day, catch, catch up with, charm,
   check in, cleanup, clear, clear profit, clock in, close with,
   collect, come, come along, come by, come in, come in for,
   come into, come on, come out first, come to, come to hand,
   come up to, come up with, complete, con, consummate, contract,
   convalesce, convince, corral, crescendo, cure, current gain, cut,
   dead time, derive, derive from, develop, development, dividend,
   dividends, drag down, draw, draw from, draw over, earn, earnings,
   edema, elevation, emolument, enhancement, enlargement,
   enter into possession, expansion, extension, fall in with,
   fall into, fetch, fetch up at, filthy lucre, find, finish in front,
   flood, fluke, fulfill, gain ground, gain on, gain over,
   gain strength, gain the day, gain upon, gains, garner, gather, get,
   get ahead, get along, get better, get in, get there, get to,
   gettings, glean, gleanings, go ahead, go forward, go up, good,
   graduate, greatening, gross, gross profit, grow, grow better,
   growth, gush, harvest, have, have coming in, heal, hike, hit,
   hit town, hoard, holdup, hook, hook in, hysteresis, improve,
   improvement, income, increase, increment, incur, inflation,
   intensify, interest, invigorate, invite, it, jump, killing, lag,
   lap, leap, leave behind, leave standing, look up, lucre, make,
   make a killing, make headway, make it, make progress, make strides,
   makings, margin, meliorate, mend, money, mount, mounting,
   multiplication, multiply, narrow the gap, neat profit, net,
   net profit, obtain, operational gain, outdistance, outpace,
   output lag, outrun, outsail, outstrip, outtalk, overhaul, overtake,
   paper profits, pass, pay, payment, pelf, percentage, perfect, perk,
   perk up, perks, perquisite, persuade, pick up, pickings, pop up,
   prevail on, prevail upon, prevail with, proceeds, process lag,
   procure, produce, productiveness, profit, profits, progress,
   proliferate, proliferation, pull down, pull in, punch in, raise,
   rake-off, rally, reach, realize, reap, receipts, receive,
   recuperate, remedy, renew, return, returns, revenue, ring in, rise,
   roll in, run, run up, sack, score, secure, sell, sell one on,
   shape up, share, shoot up, show improvement, show up, sign in,
   skyrocket, snowball, snowballing, spread, store, strengthen,
   succeed, surge, sway, swell, swelling, take, take in, take off,
   take on, take over, take the cake, take-in, talk into, talk over,
   throughput, time constants, time in, time lead, tumescence,
   turn up, up, upping, upsurge, upswing, uptrend, upturn, wangle,
   wangle into, wax, waxing, wealth, wear down, welcome, welfare,
   well-being, widen, widening, win, win out, win over,
   win the battle, win the laurels, win the palm, win the prize,
   win through, winnings, world of good, yield



V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

GAIN
       Gator Advertising and Information Network


V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

GAIN
       German Advanced Integrated Network (IBM)


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

GAIN. The word is used as synonymous with profits. (q. v.) See Fruit.