The Collaborative International Dictionary of English v.0.48:

Astragalus \As*trag"a*lus\, n. [L. See Astragal.]
   1. (Anat.) The ankle bone, or hock bone; the bone of the
      tarsus which articulates with the tibia at the ankle.
      [1913 Webster]

   2. (Bot.) A genus of papilionaceous plants, of the tribe
      Galege[ae], containing numerous species, two of which
      are called, in English, milk vetch and licorice vetch.
      Gum tragacanth is obtained from different oriental
      species, particularly the Astragalus gummifer and
      Astragalus verus.
      [1913 Webster]

   3. (Arch.) See Astragal, 1.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Astragalus
    n 1: large genus of annual or perennial herbs or shrubs of north
         temperate regions; largest genus in the family Leguminosae
         [syn: Astragalus, genus Astragalus]
    2: the bone in the ankle that articulates with the leg bones to
       form the ankle joint [syn: anklebone, astragal,
       astragalus, talus]