Source : Webster's Revised Unabridged Dictionary (1913)

Hyoscyamine \Hy`os*cy"a*mine\, n. [See {Hyoscyamus}.] (Chem.)
   An alkaloid found in henbane ({Hyoscyamus niger}), and
   regarded as its active principle. It is also found with other
   alkaloids in the thorn apple and deadly nightshade. It is
   extracted as a white crystalline substance, with a sharp,
   offensive taste. Hyoscyamine is isomeric with atropine, is
   very poisonous, and is used as a medicine for neuralgia, like
   belladonna. Called also {hyoscyamia}, {duboisine}, etc.

Source : WordNet®

hyoscyamine
     n : a poisonous crystalline alkaloid (isometric with atropine
         but more potent); used to treat excess motility of the
         gastrointestinal tract