The Collaborative International Dictionary of English v.0.48:

Obtain \Ob*tain"\, v. t. [imp. & p. p. Obtained; p. pr. & vb.
   n. Obtaining.] [F. obtenir, L. obtinere; ob (see Ob-) +
   tenere to hold. See Tenable.]
   [1913 Webster]
   1. To hold; to keep; to possess. [Obs.]
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            His mother, then, is mortal, but his Sire
            He who obtains the monarchy of heaven. --Milton.
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   2. To get hold of by effort; to gain possession of; to
      procure; to acquire, in any way.
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            Some pray for riches; riches they obtain. --Dryden.
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            By guileful fair words peace may be obtained.
                                                  --Shak.
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            It may be that I may obtain children by her. --Gen.
                                                  xvi. 2.
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   Syn: To attain; gain; procure; acquire; win; earn.

   Usage: See Attain. -- To Obtain, Get, Gain, Earn,
          Acquire. The idea of getting is common to all these
          terms. We may, indeed, with only a slight change of
          sense, substitute get for either of them; as, to get
          or to gain a prize; to get or to obtain an employment;
          to get or to earn a living; to get or to acquire a
          language. To gain is to get by striving; and as this
          is often a part of our good fortune, the word gain is
          peculiarly applicable to whatever comes to us
          fortuitously. Thus, we gain a victory, we gain a
          cause, we gain an advantage, etc. To earn is to
          deserve by labor or service; as, to earn good wages;
          to earn a triumph. Unfortunately, one does not always
          get or obtain what he has earned. To obtain implies
          desire for possession, and some effort directed to the
          attainment of that which is not immediately within our
          reach. Whatever we thus seek and get, we obtain,
          whether by our own exertions or those of others;
          whether by good or bad means; whether permanently, or
          only for a time. Thus, a man obtains an employment; he
          obtains an answer to a letter, etc. To acquire is more
          limited and specific. We acquire what comes to us
          gradually in the regular exercise of our abilities,
          while we obtain what comes in any way, provided we
          desire it. Thus, we acquire knowledge, property,
          honor, reputation, etc. What we acquire becomes, to a
          great extent, permanently our own; as, to acquire a
          language; to acquire habits of industry, etc.
          [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Obtain \Ob*tain"\, v. i.
   1. To gain or have a firm footing; to be recognized or
      established; to become prevalent or general; to prevail;
      as, the custom obtains of going to the seashore in summer.
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            Sobriety hath by use obtained to signify temperance
            in drinking.                          --Jer. Taylor.
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            The Theodosian code, several hundred years after
            Justinian's time, did obtain in the western parts of
            Europe.                               --Baker.
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   2. To prevail; to succeed. [archaic and Rare] --Evelyn.
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            So run that ye may obtain.            --1 Cor. ix.
                                                  24.
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            There is due from the judge to the advocate, some
            commendation, where causes are fair pleaded;
            especially towards the side which obtaineth not.
                                                  --Bacon.
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WordNet (r) 3.0 (2006):

obtain
    v 1: come into possession of; "How did you obtain the visa?"
    2: receive a specified treatment (abstract); "These aspects of
       civilization do not find expression or receive an
       interpretation"; "His movie received a good review"; "I got
       nothing but trouble for my good intentions" [syn: receive,
       get, find, obtain, incur]
    3: be valid, applicable, or true; "This theory still holds"
       [syn: prevail, hold, obtain]

Moby Thesaurus II by Grady Ward, 1.0:

129 Moby Thesaurus words for "obtain":
   accept, acquire, admit, annex, apply, arouse, assume, bag, be,
   be extant, be found, be in, be in existence, be in force,
   be met with, be present, be seized of, be the case, be the rage,
   be the rule, be the thing, be there, breathe, bring, bring back,
   bring forth, bring on, bring out, bring to light, buy, call for,
   call forth, call out, call up, capture, catch, chalk up,
   chase after, come by, come in for, come into, contract, contrive,
   corral, deduce, derive, derive from, dominate, drag down, drag out,
   draw, draw down, draw forth, draw from, draw on, draw out, earn,
   educe, effect, elicit, enter into possession, evoke, exist, fetch,
   fetch and carry, gain, get, get from, get out of, go after,
   go and get, go fetch, go for, go get, go to get, grasp,
   happen to be, harvest, have, have being, have coming in,
   have place, hold, induce, inspire, instigate, lead, live, make,
   motivate, net, occur, pick up, predominate, prevail, procure,
   provoke, pull down, purchase, reap, receive, reign, relate,
   retrieve, rouse, rule, run after, sack, score, secure, seize, shag,
   stand, stimulate, subsist, summon forth, summon up, superinduce,
   take, take in, take on, take over, take possession of, wangle,
   wangle out of, win, winkle out, worm out, worm out of