The Collaborative International Dictionary of English v.0.48:

Atropa \Atropa\ n.
   a genus of plants of the nightshade family, including the
   belladonna (Atropa belladonna).

   Syn: genus Atropa.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Belladonna \Bel`la*don"na\, n. [It., literally fine lady; bella
   beautiful + donna lady.] (Bot.)
   (a) An herbaceous European plant (Atropa belladonna) with
       reddish bell-shaped flowers and shining black berries.
       The whole plant and its fruit are very poisonous, and the
       root and leaves are used as powerful medicinal agents.
       Its properties are largely due to the alkaloid atropine
       which it contains. Called also deadly nightshade.
   (b) A species of Amaryllis (Amaryllis belladonna); the
       belladonna lily.
       [1913 Webster]

WordNet (r) 3.0 (2006):

belladonna
    n 1: perennial Eurasian herb with reddish bell-shaped flowers
         and shining black berries; extensively grown in United
         States; roots and leaves yield atropine [syn: belladonna,
         belladonna plant, deadly nightshade, Atropa
         belladonna]
    2: an alkaloidal extract or tincture of the poisonous belladonna
       plant that is used medicinally

Moby Thesaurus II by Grady Ward, 1.0:

38 Moby Thesaurus words for "belladonna":
   DET, DMT, Indian hemp, LSD, THC, bhang, cannabis, castor-oil plant,
   deadly nightshade, death camas, diethyltryptamine,
   dimethyltryptamine, ergot, foxglove, ganja, hallucinogens, hashish,
   hemlock, hemp, henbane, horsetail, hyoscyamus, jimsonweed,
   marijuana, mayapple, mescal, mescal bean, mescaline, monkshood,
   morning glory seeds, peyote, poison ivy, poison parsley,
   poison sumac, pokeweed, psilocin, psilocybin, stramonium



The Devil's Dictionary (1881-1906):

BELLADONNA, n.  In Italian a beautiful lady; in English a deadly
poison.  A striking example of the essential identity of the two
tongues.