The Collaborative International Dictionary of English v.0.48:

Validate \Val"i*date\, v. t. [See Valid.]
   To confirm; to render valid; to give legal force to.
   [1913 Webster]

         The chamber of deputies . . . refusing to validate at
         once the election of an official candidate. --London
                                                  Spectator.
   [1913 Webster]

WordNet (r) 3.0 (2006):

validate
    v 1: declare or make legally valid [syn: validate,
         formalize, formalise] [ant: annul, avoid,
         invalidate, nullify, quash, void]
    2: prove valid; show or confirm the validity of something [ant:
       invalidate, nullify]
    3: give evidence for [syn: validate, corroborate]
    4: make valid or confirm the validity of; "validate a ticket"
       [ant: invalidate, vitiate, void]

Moby Thesaurus II by Grady Ward, 1.0:

122 Moby Thesaurus words for "validate":
   OK, accept, accredit, affirm, amen, approve, assay, attest, audit,
   authenticate, authorize, autograph, back, back up, bear out,
   bolster, bring to test, buttress, certificate, certify, charter,
   check, check and doublecheck, check out, check over,
   circumstantiate, collate, confirm, constitute, corroborate, cosign,
   countersign, cross-check, cut and try, declare lawful, decree,
   document, double-check, empower, enable, enact, endorse,
   enfranchise, entitle, essay, establish, experiment, formulate,
   fortify, franchise, give a try, give a tryout,
   give official sanction, give permission, give power,
   give the go-ahead, give the imprimatur, give thumbs up, have a go,
   initial, justify, legalize, legislate, legitimate, legitimatize,
   legitimize, license, make a regulation, make legal, notarize,
   ordain, pass, pass on, pass upon, patent, permit, play around with,
   practice upon, prescribe, privilege, probate, prove, put in force,
   put to trial, ratify, recheck, regulate, reinforce, research,
   road-test, rubber stamp, rubber-stamp, run a sample, sample,
   sanction, say amen to, seal, second, shake down, sign,
   sign and seal, strengthen, subscribe to, substantiate, support,
   sustain, swear and affirm, swear to, taste, test, triple-check,
   try, try it on, try out, undergird, undersign, underwrite, uphold,
   verify, visa, vise, warrant