The Collaborative International Dictionary of English v.0.48:

Invent \In*vent"\, v. t. [imp. & p. p. Invented; p. pr. & vb.
   n. Inventing.] [L. inventus, p. p. of invenire to come
   upon, to find, invent; pref. in- in + venire to come, akin to
   E. come: cf. F. inventer. See Come.]
   [1913 Webster]
   1. To come or light upon; to meet; to find. [Obs.]
      [1913 Webster]

            And vowed never to return again,
            Till him alive or dead she did invent. --Spenser.
      [1913 Webster]

   2. To discover, as by study or inquiry; to find out; to
      devise; to contrive or produce for the first time; --
      applied commonly to the discovery of some serviceable
      mode, instrument, or machine.
      [1913 Webster]

            Thus first Necessity invented stools. --Cowper.
      [1913 Webster]

   3. To frame by the imagination; to fabricate mentally; to
      forge; -- in a good or a bad sense; as, to invent the
      machinery of a poem; to invent a falsehood.
      [1913 Webster]

            Whate'er his cruel malice could invent. --Milton.
      [1913 Webster]

            He had invented some circumstances, and put the
            worst possible construction on others. --Sir W.
                                                  Scott.

   Syn: To discover; contrive; devise; frame; design; fabricate;
        concoct; elaborate. See Discover.
        [1913 Webster]

WordNet (r) 3.0 (2006):

invent
    v 1: come up with (an idea, plan, explanation, theory, or
         principle) after a mental effort; "excogitate a way to
         measure the speed of light" [syn: invent, contrive,
         devise, excogitate, formulate, forge]
    2: make up something artificial or untrue [syn: fabricate,
       manufacture, cook up, make up, invent]

Moby Thesaurus II by Grady Ward, 1.0:

99 Moby Thesaurus words for "invent":
   beget, break ground, break the ice, breed, bring forth,
   bring into being, call into being, coin, conceit, conceive,
   conceptualize, concoct, contrive, cook up, counterfeit, create,
   design, determine, develop, devise, discover, dream up, engender,
   envision, evolve, experience imaginatively, fabricate, fake, fancy,
   fantasize, fictionalize, find, find out, forge, formulate, frame,
   fudge, generate, get, give being to, give rise to, hatch, hatch up,
   head, head up, hit, hit upon, hoke up, hunt down, ideate, imagine,
   improvise, inaugurate, initiate, innovate, introduce,
   introduce new blood, lead, lead off, lead the way, locate,
   make do with, make innovations, make up, manufacture, mature, mint,
   mold, neologize, neoterize, originate, pioneer, plan, precede,
   procreate, produce, rediscover, renew, renovate, revolutionize,
   run down, run to earth, shape, spawn, stand first, strike,
   strike out, suppose, take the initiative, take the lead,
   take the plunge, think out, think up, trace, trace down,
   track down, trump up, turn out, vamp up