Source : Webster's Revised Unabridged Dictionary (1913)

Nightshade \Night"shade`\, n. [AS. nichtscadu.] (Bot.)
   A common name of many species of the genus {Solanum}, given
   esp. to the {Solanum nigrum}, or black nightshade, a low,
   branching weed with small white flowers and black berries
   reputed to be poisonous.

   {Deadly nightshade}. Same as {Belladonna}
   (a) .

   {Enchanter's nightshade}. See under {Enchanter}.

   {Stinking nightshade}. See {Henbane}.

   {Three-leaved nightshade}. See {Trillium}.

Deadly \Dead"ly\, a.
   1. Capable of causing death; mortal; fatal; destructive;
      certain or likely to cause death; as, a deadly blow or
      wound.

   2. Aiming or willing to destroy; implacable; desperately
      hostile; flagitious; as, deadly enemies.

            Thy assailant is quick, skillful, and deadly.
                                                  --Shak.

   3. Subject to death; mortal. [Obs.]

            The image of a deadly man.            --Wyclif (Rom.
                                                  i. 23).

   {Deadly nightshade} (Bot.), a poisonous plant; belladonna.
      See under {Nightshade}.

Source : WordNet®

deadly nightshade
     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},
           {Atropa belladonna}]
     2: poisonous perennial Old World vine having violet flowers and
        oval coral-red berries; widespread weed in North America
        [syn: {bittersweet}, {bittersweet nightshade}, {climbing
        nightshade}, {poisonous nightshade}, {woody nightshade}, {Solanum
        dulcamara}]