The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Hyoscyamus \Hy`os*cy"a*mus\, n. [L., fr. Gr. ?; ? a sow, hog + ?
   a bean.]
   1. (Bot.) A genus of poisonous plants of the Nightshade
      family; henbane.
      [1913 Webster]

   2. (Med.) The leaves of the black henbane (Hyoscyamus
      niger), used in neuralgic and pectorial troubles.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Henbane \Hen"bane`\, n. [Hen + bane.] (Bot.)
   A plant of the genus Hyoscyamus (Hyoscyamus niger). All
   parts of the plant are poisonous, and the leaves are used for
   the same purposes as belladonna. It is poisonous to domestic
   fowls; whence the name. Called also, stinking nightshade,
   from the fetid odor of the plant. See Hyoscyamus.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Hyoscyamus niger
    n 1: poisonous fetid Old World herb having sticky hairy leaves
         and yellow-brown flowers; yields hyoscyamine and
         scopolamine [syn: henbane, black henbane, stinking
         nightshade, Hyoscyamus niger]