adjective

not based on any good reason.

your fears are quite groundless

baseless,without basis,without foundation,foundationless,ill-founded,unfounded,unsupported,uncorroborated,unproven,not backed up,empty,idle,vain,chimerical,imaginary,illusory,false,unsubstantiated,unwarranted,unjustified,unjustifiable,uncalled for,unprovoked,without cause,without reason,without justification,unreasonable,irrational,illogical,unsound,unreliable,questionable,misguided,spurious,specious,fallacious,erroneous