Synonyms of uncorroborated

2 Syllables
flimsy, groundless
3 Syllables
bottomless, ungrounded, baseless, gratuitous, reasonless, unfounded
4 Syllables
unwarranted, untenable, unjustified, unofficial, foundationless, unconfirmed, unsupported
5 Syllables
unjustifiable, unsubstantiated