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]

Moby Thesaurus II by Grady Ward, 1.0:

43 Moby Thesaurus words for "substantiated":
   actual, ascertained, attested, authenticated, borne out,
   categorically true, certain, certified, circumstantiated,
   confirmed, corroborated, demonstrated, determined, documentary,
   effectual, established, factual, fixed, historical, not in error,
   objectively true, proved, proven, real, settled, shown,
   sure-enough, true, true as gospel, truthful, unconfuted, undenied,
   undoubted, unerroneous, unfallacious, unfalse, unmistaken,
   unquestionable, unrefuted, validated, veracious, verified,
   veritable