Meaning

noun a worthless lazy fellow

noun large somewhat primitive fish-eating diving bird of the northern hemisphere having webbed feet placed far back; related to the grebes

noun a person with confused ideas; incapable of serious thought

originFrom Middle English louen, lowen (“rascal; rogue”), probably of Middle Dutch or Middle Low German origin. Compare Dutch loen (“simpleton”). Or, related to etymology 2, due to the bird's loud cry. Folk etymology associates it slang-wise with lunatic, though the latter may have influenced it; see loony.

Etymology from Wiktionary, CC BY-SA 3.0