Source : Webster's Revised Unabridged Dictionary (1913)

Capsaicin \Cap*sa"i*cin\, n. [From {Capsicum}.] (Chem.)
   A colorless crystalline substance extracted from the
   {Capsicum annuum}, and giving off vapors of intense acridity.

Source : WordNet®

capsaicin
     n : colorless pungent crystalline compound derived from
         capsicum; source of the hotness of hot peppers of the
         genus Capsicum such as chili and cayenne and jalapeno