(a.) Without ground or foundation; wanting cause or reason for support; not authorized; false; as, groundless fear; a groundless report or assertion.

baseless bottomless built on sand chimerical empty flimsy gratuitous hypothetical idle ill-founded illusory imaginary inconclusive indecisive not following not proved not well-founded speculative suppositional tenuous unascertained unattested unauthenticated unbased uncalled-for uncertified unconfirmed uncorroborated undemonstrated undetermined unestablished unfixed unfounded ungrounded unjustifiable unjustified unproved unproven unreasonable unsettled unshown unsound unsubstantiated unsupportable unsupported unsupported by evidence unsustainable unsustained untenable untested untried unvalidated unverified unwarranted vain without basis without foundation without grounds