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]

WordNet (r) 3.0 (2006):

Hyoscyamus
    n 1: genus of poisonous herbs: henbane [syn: Hyoscyamus,
         genus Hyoscyamus]