a colorless, crystalline, very poisonous alkaloid, CHNO, obtained from henbane and other plants of the nightshade family: it is used in medicine as a sedative, antispasmodic, etc.
See hyoscyamine in American Heritage Dictionary 4
(hīˌə-sīˈə-mēnˌ)
noun
A poisonous white crystalline alkaloid, C17H23NO3, isometric with atropine and having similar uses but more potent effects.