loon, loun noun, also in diminutive loonie a boy, young man in North East Scotland, Perthshire and Fife, 17-. etymology: Scots; from Older Scots loun ‘a rogue, a rascal’ from 1470 ‘a strumpet’, ante 1568 ‘a fellow’; Middle English lowen ‘a rogue’; Middle Dutch loen ‘a fool, a stupid fellow, a lout’; also collected by EMcC/PS; attested by BS in TDITA, JS and BW note:

Lexicon Balatronicum (1811) attests the forms Loon, or Lout A country bumpkin, or clown.