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):

substantiating
    adj 1: serving to support or corroborate; "collateral evidence"
           [syn: collateral, confirmative, confirming,
           confirmatory, corroborative, corroboratory,
           substantiating, substantiative, validating,
           validatory, verificatory, verifying]