The Collaborative International Dictionary of English v.0.48:

Beaver \Bea"ver\, n. [OE. bever, AS. beofer, befer; akin to D.
   bever, OHG. bibar, G. biber, Sw. b[aum]fver, Dan. b[ae]ver,
   Lith. bebru, Russ. bobr', Gael. beabhar, Corn. befer, L.
   fiber, and Skr. babhrus large ichneumon; also as an adj.,
   brown, the animal being probably named from its color.
   [root]253. See Brown.]
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   1. (Zool.) An amphibious rodent, of the genus Castor.
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   Note: It has palmated hind feet, and a broad, flat tail. It
         is remarkable for its ingenuity in constructing its
         lodges or "houses," and dams across streams. It is
         valued for its fur, and for the material called
         castor, obtained from two small bags in the groin of
         the animal. The European species is Castor fiber, and
         the American is generally considered a variety of this,
         although sometimes called Castor Canadensis.
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   2. The fur of the beaver.
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   3. A hat, formerly made of the fur of the beaver, but now
      usually of silk.
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            A brown beaver slouched over his eyes. --Prescott.
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   4. Beaver cloth, a heavy felted woolen cloth, used chiefly
      for making overcoats.
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   5. A man's beard.
      [PJC]

   6. The hair on a woman's pubic area; -- vulgar. [vulgar
      slang]
      [PJC]

   7. A woman; -- vulgar and offensive. [vulgar slang]
      [PJC]

   8. A person who works enthusiastically and diligently; --
      used especially in the phrase eager beaver. [informal]
      [PJC]

   Beaver rat (Zool.), an aquatic ratlike quadruped of
      Tasmania (Hydromys chrysogaster).

   Beaver skin, the furry skin of the beaver.

   Bank beaver. See under 1st Bank.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Castor canadensis
    n 1: a variety of beaver found in almost all areas of North
         America except Florida [syn: New World beaver, Castor
         canadensis]