The Collaborative International Dictionary of English v.0.48:

Milk vetch \Milk" vetch`\ (Bot.)
   A leguminous herb (Astragalus glycyphyllos) of Europe and
   Asia, supposed to increase the secretion of milk in goats.
   [1913 Webster]

   Note: The name is sometimes taken for the whole genus
         Astragalus, of which there are about two hundred
         species in North America, and even more elsewhere.
         [1913 Webster]

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):

milk vetch
    n 1: any of various plants of the genus Astragalus [syn: milk
         vetch, milk-vetch]