atropine
    n 1: a poisonous crystalline alkaloid extracted from the
         nightshade family; used as an antispasmodic and to dilate
         the eye pupil; also administered in large amounts as an
         antidote for organophosphate nerve agents or
         organophosphate insecticides

Atropine \At"ro*pine\, n. [Gr. ? inflexible; hence ? ?, one of
   the three Parc[ae]; 'a priv. + ? to turn.] (Chem.)
   A poisonous, white, crystallizable alkaloid, extracted from
   the Atropa belladonna, or deadly nightshade, and the
   Datura Stramonium, or thorn apple. It is remarkable for its
   power in dilating the pupil of the eye. Called also
   daturine.
   [1913 Webster]