loon /luːn/ BrE AmE noun [countable]
[ Sense 1: Date: 1600-1700 ; Origin: From a Scandinavian language. ]
[ Sense 2: Date: 1600-1700 ; Origin: loun 'bad person' (15-19 centuries) (influenced by ⇨ ↑ loon (1) (because of its wild sound) and by ⇨ ↑ loony 1 ) ]
1 . a large North American bird that eats fish and that makes a long high sound
2 . informal a silly or strange person – used humorously