From The Collaborative International Dictionary of English v.0.48:
Loon \Loon\ (l[=oo]n), n. [Scot. loun, lown, loon; akin to OD.
loen a stupid man; prob. for an older lown, and akin to E.
lame.]
A sorry fellow; a worthless person; a rogue.
[1913 Webster]
From The Collaborative International Dictionary of English v.0.48:
Loon \Loon\, n. [For older loom, Icel. l[=o]mr; akin to Dan. &
Sw. lom.] (Zool.)
Any one of several aquatic, wed-footed, northern birds of the
genus Urinator (formerly Colymbus), noted for their
expertness in diving and swimming under water. The common
loon, or great northern diver (Urinator imber, or Colymbus
torquatus), and the red-throated loon or diver (Urinator
septentrionalis), are the best known species. See Diver.
[1913 Webster]