loon

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of several fish-eating diving birds of the genus Gavia of northern regions, having a short tail, webbed feet, and a laughlike cry.
• noun One who is crazy or deranged.

from The Century Dictionary.

• noun A stupid fellow; a clown: with various shades of intensity as an opprobrious epithet, like fool, dolt, etc.
• noun A four-toed diving bird of the genus Colymbus or Urinator. See Colymbidæ.
• noun A name used locally for several very different birds: in England, for some of the grebes, including the large Podiceps cristatus and the little dabchick, P. minor; by sailors often in the form loom, for the murre, Lomvia arra.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Zoöl.) 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.
• noun A sorry fellow; a worthless person; a rogue.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Any of various birds, of the order Gaviiformes, of North America and Europe that dive for fish and have a short tail, webbed feet and a yodeling cry.
• noun idler, lout
• noun Ulster boy, lad
• noun harlot; mistress
• noun simpleton; (also (slang)) crazy or deranged person.
• noun Ireland English Soldier of an expeditionary army in Ireland.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• 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