The Collaborative International Dictionary of English v.0.48:

Thymol \Thym"ol\, n. [Thyme + -ol.] (Chem.)
   A phenol derivative of cymene, C10H13.OH, isomeric with
   carvacrol, found in oil of thyme, and extracted as a white
   crystalline substance of a pleasant aromatic odor and strong
   antiseptic properties; -- called also hydroxy cymene.
   [1913 Webster]

WordNet (r) 3.0 (2006):

thymol
    n 1: a colorless crystalline solid used in perfume or preserving
         biological specimens or in embalming or medically as a
         fungicide or antiseptic [syn: thymol, thyme camphor,
         thymic acid]