resulting from or showing a lack of sense; ill-considered; unwise

a foolish action, a foolish speech.

lacking forethought or caution.

trifling, insignificant, or paltry.

adjective

careful , cautious , circumspect , prudent , sensible , serious , thoughtful , unfoolish , wise

adjective

absurd , asinine , brainless , cockamamy , crazy , daffy * , daft , dippy , doltish , dotty * , fantastic , fatuous , feebleminded * , half-baked * , half-witted * , harebrained * , ill-advised , ill-considered , imbecilic , imprudent , incautious , indiscreet , injudicious , insane , irrational , jerky * , kooky , loony * , ludicrous , lunatic , mad , moronic , nerdy , nutty * , preposterous , ridiculous , senseless , short-sighted , silly , simple , stupid , unintelligent , unreasonable , unwise , wacky * , weak , witless , zany * , insensate , weak-minded , harebrained , idiotic , nonsensical , softheaded , tomfool , unearthly , zany , anile , anserine , batty , boneheaded , cockeyed , dizzy , doddering , dumb , fatuitous , goofy , half-witted , heedless , imbecile , inane , inept , insagacious , loony , nutty , puerile , rash