The Collaborative International Dictionary of English v.0.48:

Ratify \Rat"i*fy\ (r[a^]t"[i^]*f[imac]), v. t. [imp. & p. p.
   Ratified (r[a^]t"[i^]*f[imac]d); p. pr. & vb. n.
   Ratifying (r[a^]t"[i^]*f[imac]`[i^]ng).] [F. ratifier, fr.
   L. ratus fixed by calculation, firm, valid + -ficare (in
   comp.) to make. See Rate, n., and -fy.]
   To approve and sanction; to make valid; to confirm; to
   establish; to settle; especially, to give sanction to, as
   something done by an agent or servant; as, to ratify an
   agreement, treaty, or contract; to ratify a nomination.
   [1913 Webster]

         It is impossible for the divine power to set a seal to
         a lie by ratifying an imposture with such a miracle.
                                                  --South.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ratify
    v 1: approve and express assent, responsibility, or obligation;
         "All parties ratified the peace treaty"; "Have you signed
         your contract yet?" [syn: sign, ratify]

Moby Thesaurus II by Grady Ward, 1.0:

114 Moby Thesaurus words for "ratify":
   OK, accede to, accept, accord to, accredit, adopt, affiliate,
   affirm, agree to, amen, approve, approve of, assent, attest,
   authenticate, authorize, autograph, back, back up, be willing,
   bear out, bolster, buttress, carry, certificate, certify, charter,
   circumstantiate, clinch, commission, condescend, confirm,
   connive at, consent, consent to silently, corroborate, cosign,
   countersign, deign, document, embrace, empower, enable, endorse,
   enfranchise, ensure, entitle, espouse, establish, fortify,
   franchise, give consent, give official sanction, give permission,
   give power, give the go-ahead, give the imprimatur, give thumbs up,
   go along with, go in for, grant, guarantee, have no objection,
   hold with, initial, legalize, legitimize, license, nod, nod assent,
   not refuse, notarize, okay, pass, pass on, pass upon, patent,
   permit, privilege, probate, prove, reinforce, rubber stamp,
   sanction, say amen to, say aye, say yes, seal, second, settle,
   sign, sign and seal, strengthen, subscribe to, substantiate,
   support, sustain, swear and affirm, swear to, take kindly to,
   take up, undergird, undersign, underwrite, uphold, validate,
   verify, visa, vise, vote affirmatively, vote aye, warrant, wink at,
   yield assent