ill-founded 
adjective
(Especially of an idea or belief) not based on fact or reliable evidence: ill-founded criticism her fear may be ill-founded...
- Subsequent campaigns showed that this belief was ill-founded.
- This is an insulting and ill-founded belief which I would advise you to reconsider.
- Therefore, I conclude that the Warsaw Convention applies to this case and that the plaintiff's claim based on misrepresentation is ill-founded, both in fact and in law.
Synonyms
baseless, groundless, without foundation, foundationless, without basis, unjustified, unsupported;
unsubstantiated, unproven, unverified, uncorroborated, unconfirmed, unauthenticated, not backed up by evidence, speculative, conjectural;
unsound, unreliable, questionable, misinformed, misguided, spurious, trumped-up