The Collaborative International Dictionary of English v.0.48:

Cymene \Cy"mene\ (s?"m?n), n. (Chem.)
   A colorless, liquid, combustible hydrocarbon,
   CH3.C6H4.C3H7, of pleasant odor, obtained from oil of
   cumin, oil of caraway, carvacrol, camphor, etc.; -- called
   also paracymene, and formerly camphogen.
   [1913 Webster]

WordNet (r) 3.0 (2006):

cymene
    n 1: any of three isotopes of a colorless aromatic liquid
         hydrocarbon occurring in the volatile oil of cumin and
         thyme and used in the manufacture of synthetic resins