1 as daft as a brush (informal, chiefly Brit.) barking (slang) barking mad (slang) crackpot (informal) crazed, crazy, demented, deranged, doolally (slang) gaga (informal) gonzo (slang) loopy (informal) mad, mentally disordered, mentally ill, non compos mentis, not the full shilling (informal) off one's trolley (slang) of unsound mind, out of one's mind, out to lunch (informal) unhinged, up the pole (informal) wacko or whacko (informal)
2 barking (slang) barking mad (slang) barmy (slang) batty (slang) bonkers (slang, chiefly Brit.) cracked (slang) crackers (Brit. slang) cuckoo (informal) having a screw loose (informal) loony (slang) loopy (informal) mental (slang) not right in the head, nuts (slang) nutty (slang) off one's chump (slang) off one's head (slang) off one's nut (slang) off one's rocker (slang) off one's trolley (slang) round the bend (informal) round the twist (informal) screwy (informal)
3 bizarre, daft (informal) fatuous, foolish, idiotic, impractical, inane, irrational, irresponsible, lunatic, preposterous, senseless, stupid
Antonyms
logical, lucid, normal, practical, rational, reasonable, reasoned, sane, sensible, sound