adjective

rash; ill-judged.

a hare-brained scheme

ill-judged,rash,foolish,foolhardy,reckless,madcap,wild,silly,stupid,ridiculous,preposterous,absurd,idiotic,asinine,imprudent,impracticable,unworkable,unrealistic,unconsidered,half-baked,ill-thought-out,ill-advised,ill-conceived,crackpot,crackbrained,cock-eyed,crazy,daft,barmy,unintelligent,empty-headed,scatterbrained,feather-brained,birdbrained,pea-brained,brainless,giddy,dippy,dizzy,dopey,airheaded,dappy,dotty