The Collaborative International Dictionary of English v.0.48:

Unsubstantiated \Unsubstantiated\
   See substantiated.

WordNet (r) 3.0 (2006):

unsubstantiated
    adj 1: unsupported by other evidence [syn: uncorroborated,
           unsubstantiated]

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "unsubstantiated":
   groundless, inconclusive, indecisive, not following, not proved,
   unascertained, unattested, unauthenticated, uncertified,
   unconfirmed, uncorroborated, undemonstrated, undetermined,
   unestablished, unfixed, unfounded, unproved, unproven, unsettled,
   unshown, unsupported, unsupported by evidence, unsustained,
   untested, untried, unvalidated, unverified, without basis,
   without grounds