I. ˈlün noun
Etymology: Middle English loun
Date: 15th century
1. : lout , idler
2. chiefly Scottish : boy
3.
a. : a crazy person
b. : simpleton
II. noun
Etymology: of Scandinavian origin; akin to Old Norse lōmr loon
Date: 1634
: any of several large birds (genus Gavia of the family Gaviidae) of Holarctic regions that feed on fish by diving and have their legs placed far back under the body for optimal locomotion underwater