LOON Meaning of LOON in English n. 1 US any aquatic diving bird of the family Gaviidae, with a long slender body and a sharp bill; a diver. 2 colloq. a crazy person (cf. LOONY). [ alt. f. loom f. ON lómr ] Concise Oxford English dictionary. Краткий оксфордский словарь английского языка. 2012