loon

American Heritage® Dictionary of the English Language, Fourth Edition

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

Century Dictionary and Cyclopedia

1. n. A stupid fellow; a clown: with various shades of intensity as an opprobrious epithet, like fool, dolt, etc.
2. n. A four-toed diving bird of the genus Colymbus or Urinator. See Colymbidæ. There are several species, all inhabiting the northern hemisphere. The great northern diver, ring-necked loon, or ember-goose, C. torquatus or C. glacialis or Urinator imber, is from 30 to 36 inches long, and 4½ feet in stretch of wings; when adult it is glossy-black with greenish and purplish metallic reflections on the head and neck, which, with the back, are marked regularly with white spots. The under parts are white, and the bill is black. C. adamsi, the yellow-billed loon, is somewhat larger. The black-throated loon or diver, C. arcticus, resembles the foregoing, but is smaller, with much of the head clear bluish-gray. The red-throated loon, C. septentrionalis, is much like C. arcticus, but is smaller still, and has a chestnut patch on the throat. Both the two smaller loons, the red- and the black-throated, are also called speckled loons, and a variety of the former, from the western coast of North America, is recognized as C. pacificus. (See diver, 1 .) The wild actions of the loon in escaping danger and its dismal cry (see looning) suggest the idea of insanity; whence the common (American) simile “as crazy as a loon.”
3. n. 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.

Wiktionary

1. n. 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.
2. n. idler, lout
3. n. Ulster boy, lad
4. n. harlot; mistress
5. n. simpleton; (also (slang)) crazy or deranged person.
6. n. Ireland English Soldier of an expeditionary army in Ireland.

GNU Webster's 1913

1. n. A sorry fellow; a worthless person; a rogue.
2. n. (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.

WordNet 3.0

1. n. a worthless lazy fellow
2. n. large somewhat primitive fish-eating diving bird of the northern hemisphere having webbed feet placed far back; related to the grebes
3. n. a person with confused ideas; incapable of serious thought