Source : Webster's Revised Unabridged Dictionary (1913)

Pyrene \Py"rene\, n. [Gr. ? fire.] (Chem.)
   One of the less volatile hydrocarbons of coal tar, obtained
   as a white crystalline substance, {C16H10}.

Pyrene \Py"rene\, n. (Bot.)
   Same as {Pyrena}.

Source : WordNet®

pyrene
     n 1: a pale yellow crystalline hydrocarbon C16H10 extracted from
          coal tar
     2: the small hard nutlet of a drupe or drupelet; the seed and
        the hard endocarp that surrounds it