- insane - afflicted with or characteristic of mental derangement; "was declared insane"; "insane laughter"
Antonyms: sane, compos mentis, of sound mind, in his right mind, in her right mind, in their right minds, lucid
- harebrained, insane, mad - very foolish; "harebrained ideas"; "took insane risks behind the wheel"; "a completely mad scheme to build a bridge between two mountains"
Antonym: wise (indirect, via foolish)