The Collaborative International Dictionary of English v.0.48:

Tragacanth \Trag"a*canth\, n. [L. tragacanthum tragacanth,
   tragacantha the plant producing tragacanth, Gr. ? ? a he-goat
   + ? a thorn: cf. F. tragacanthe.]
   A kind of gum procured from a spiny leguminous shrub
   (Astragalus gummifer) of Western Asia, and other species of
   Astragalus. It comes in hard whitish or yellowish flakes or
   filaments, and is nearly insoluble in water, but slowly
   swells into a mucilaginous mass, which is used as a
   substitute for gum arabic in medicine and the arts. Called
   also gum tragacanth.
   [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]