loony(noun, adjective) adjective1. (of a person) insane.Similar word(s): insane, balmy, barmy, bats, batty, bonkers, buggy, cracked, crackers, daft, dotty, fruity, haywire, kookie, kooky, loopy, nuts, nutty, wacky, whacky2. (of a thing) very silly, absurd. noun1. someone deranged and possibly dangerousSimilar word(s): crazy, looney, nutcase, weirdoDefinition categories: person, lunatic, madman, maniac