The Collaborative International Dictionary of English v.0.48:

Substantiate \Sub*stan"ti*ate\, v. t. [imp. & p. p.
   Substantiated; p. pr. & vb. n. Substantiating.]
   1. To make to exist; to make real. --Ayliffe.
      [1913 Webster]

   2. To establish the existence or truth of by proof or
      competent evidence; to verify; as, to substantiate a
      charge or allegation; to substantiate a declaration.
      [1913 Webster]

            Observation is, in turn, wanted to direct and
            substantiate the course of experiment. --Coleridge.
      [1913 Webster]

WordNet (r) 3.0 (2006):

substantiate
    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: represent in bodily form; "He embodies all that is evil wrong
       with the system"; "The painting substantiates the feelings of
       the artist" [syn: incarnate, body forth, embody,
       substantiate]
    3: make real or concrete; give reality or substance to; "our
       ideas must be substantiated into actions" [syn: realize,
       realise, actualize, actualise, substantiate]
    4: solidify, firm, or strengthen; "The president's trip will
       substantiate good relations with the former enemy country"