Source : Webster's Revised Unabridged Dictionary (1913)

Nicotine \Nic"o*tine\ (? or ?), n. [F. nicotine. See
   {Nicotian}.] (Chem.)
   An alkaloid which is the active principle of tobacco. It is a
   colorless, transparent, oily liquid, having an acrid odor,
   and an acrid burning taste. It is intensely poisonous. --Ure.

Source : WordNet®

nicotine
     n : an alkaloid poison that occurs in tobacco; used in medicine
         and as an insecticide