The Collaborative International Dictionary of English v.0.48:

Ungrounded \Ungrounded\
   See grounded.

Moby Thesaurus II by Grady Ward, 1.0:

18 Moby Thesaurus words for "ungrounded":
   baseless, built on sand, empty, groundless, idle, ill-founded,
   not well-founded, unbased, unfounded, unsupportable, unsupported,
   unsustainable, unsustained, untenable, unwarranted, vain,
   without basis, without foundation