From Longman Dictionary of Contemporary Englishloonloon /luːn/ noun [countable] 1 HBBa large North American bird that eats fish and that makes a long high sound2 STRANGE informal a silly or strange person – used humorously
Examples from the Corpus
loon• Rosie, the woman is crazy as a loon.• Would you laugh like a loon at such stupid things?• Why add them, with their evocation of the doddering loon, slumped, with listless ear-trumpet, over the board table?• All the eye can see are evergreens, a placid body of water and the occasional loon.• The princess in the tower, the loon in the attic!Origin loon 1. (1600-1700) From a Scandinavian language. 2. (1600-1700) loun “bad person” ((15-19 centuries)) (influenced by → LOON1 (because of its wild sound) and by → LOONY1) 