loon (n.1)youdaoicibaDictYouDict
large diving bird (especially the Great Northern Diver), 1630s, from a Scandinavian source (compare Norwegian lom, from Old Norse lomr).
loon (n.2)youdaoicibaDictYouDict
"crazy person," mid-15c., lowen "rascal," of uncertain origin, perhaps related to Dutch loen "stupid person."