Synonyms of foundationless

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