adj. 25B6; adjective BASELESS, without basis, without foundation, ill-founded, unfounded, unsupported, uncorroborated, unproven, empty, idle, unsubstantiated, unwarranted, unjustified, unjustifiable, without cause, without reason, without justification, unreasonable, irrational, illogical, misguided.
GROUNDLESS
Meaning of GROUNDLESS in English
Concise Oxford thesaurus English vocabulary. Краткий оксфордский словарь английского языка тезаурус. 2012