The Collaborative International Dictionary of English v.0.48:

Corroborate \Cor*rob"o*rate\ (k?r-r?b"?-r?t), v. t. [imp. & p.
   p. Corroborated (-r?`t?d); p. pr. & vb. n. Corroborating
   (-r?`t?ng). ] [L. corroboratus, p. p. of corroborare to
   corroborate; cor- + roborare to strengthen, robur strength.
   See Robust.]
   1. To make strong, or to give additional strength to; to
      strengthen. [Obs.]
      [1913 Webster]

            As any limb well and duly exercised, grows stronger,
            the nerves of the body are corroborated thereby.
                                                  --I. Watts.
      [1913 Webster]

   2. To make more certain; to confirm; to establish.
      [1913 Webster]

            The concurrence of all corroborates the same truth.
                                                  --I. Taylor.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Corroborate \Cor*rob"o*rate\ (-r?t), a.
   Corroborated. [Obs.] --Bacon.
   [1913 Webster]

WordNet (r) 3.0 (2006):

corroborate
    v 1: establish or strengthen as with new evidence or facts; "his
         story confirmed my doubts"; "The evidence supports the
         defendant" [syn: confirm, corroborate, sustain,
         substantiate, support, affirm] [ant: contradict,
         negate]
    2: give evidence for [syn: validate, corroborate]
    3: support with evidence or authority or make more certain or
       confirm; "The stories and claims were born out by the
       evidence" [syn: corroborate, underpin, bear out,
       support]

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "corroborate":
   affirm, attest, authenticate, back, back up, bear out, bolster,
   buttress, certify, circumstantiate, confirm, document, fortify,
   justify, probate, prove, ratify, reinforce, strengthen,
   substantiate, support, sustain, undergird, uphold, validate,
   verify, warrant