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:

Dracanth \Dra"canth\, n.
   A kind of gum; -- called also gum tragacanth, or
   tragacanth. See Tragacanth.
   [1913 Webster]

WordNet (r) 3.0 (2006):

tragacanth
    n 1: a gum used in pharmacy, adhesives, and textile printing