loony (adj.)

also loonie, looney, luny, "crazy; silly and eccentric," 1853, American English, short for lunatic, but also influenced by loon (n.2) and perhaps loon (n.1), the bird being noted for its wild cry and method of escaping from danger. As a noun by 1884, from the adjective.

Slang loony bin "insane asylum" is by 1909. Looney left in reference to holders of political views felt to be left-wing in the extreme is from 1977. Looney Tunes, Warner Bros. studios' animated cartoon series, dates from 1930.

updated on January 03, 2019

Definitions of loony from WordNet
loony (n.)
someone deranged and possibly dangerous;
Synonyms: crazy / looney / nutcase / weirdo
loony (adj.)
informal or slang terms for mentally irregular;
Synonyms: balmy / barmy / bats / batty / bonkers / buggy / cracked / crackers / daft / dotty / fruity / haywire / kooky / kookie / loco / loopy / nuts / nutty / round the bend / around the bend / wacky / whacky
Etymologies are not definitions. From, not affiliated with etymonline.