The Collaborative International Dictionary of English v.0.48:

Verify \Ver"i*fy\ (v[e^]r"[i^]*f[imac]), v. t. [imp. & p. p.
   Verified; p. pr. & vb. n. Verifying.] [F. v['e]rifier,
   LL. verificare, from L. verus true + -ficare to make. See
   Very, and -fy.]
   1. To prove to be true or correct; to establish the truth of;
      to confirm; to substantiate.
      [1913 Webster]

            This is verified by a number of examples. --Bacon.
      [1913 Webster]

            So shalt thou best fulfill, best verify.
            The prophets old, who sung thy endless reign.
                                                  --Milton.
      [1913 Webster]

   2. To confirm or establish the authenticity of by examination
      or competent evidence; to authenticate; as, to verify a
      written statement; to verify an account, a pleading, or
      the like.
      [1913 Webster]

            To verify our title with their lives. --Shak.
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   3. To maintain; to affirm; to support. [Obs.] --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

verify
    v 1: confirm the truth of; "Please verify that the doors are
         closed"; "verify a claim"
    2: check or regulate (a scientific experiment) by conducting a
       parallel experiment or comparing with another standard; "Are
       you controlling for the temperature?" [syn: control,
       verify]
    3: attach or append a legal verification to (a pleading or
       petition)
    4: to declare or affirm solemnly and formally as true; "Before
       God I swear I am innocent" [syn: affirm, verify,
       assert, avow, aver, swan, swear]

Moby Thesaurus II by Grady Ward, 1.0:

73 Moby Thesaurus words for "verify":
   affirm, assay, attest, audit, authenticate, back, back up, balance,
   balance the books, bear out, bolster, bring to test, buttress,
   certify, check, check and doublecheck, check out, check over,
   circumstantiate, clench, clinch, collate, confirm, corroborate,
   cross-check, cut and try, demonstrate, document, double-check,
   essay, establish, experiment, fortify, give a try, give a tryout,
   guarantee, have a go, inventory, justify, overhaul,
   painstakingly match, play around with, practice upon, probate,
   prove, put to trial, ratify, recheck, reinforce, research,
   road-test, run a sample, sample, scrutinize comparatively, settle,
   shake down, show, strengthen, substantiate, support, sustain,
   take stock, taste, test, triple-check, try, try it on, try out,
   undergird, uphold, validate, vouch for, warrant