The Collaborative International Dictionary of English v.0.48:

Substantiation \Sub*stan`ti*a"tion\, n.
   The act of substantiating or proving; evidence; proof.
   [1913 Webster]

WordNet (r) 3.0 (2006):

substantiation
    n 1: additional proof that something that was believed (some
         fact or hypothesis or theory) is correct; "fossils provided
         further confirmation of the evolutionary theory" [syn:
         confirmation, verification, check, substantiation]
    2: the act of validating; finding or testing the truth of
       something [syn: validation, proof, substantiation]