Source : Webster's Revised Unabridged Dictionary (1913)

Xylene \Xy"lene\, n. [Gr. xy`lon wood.] (Chem.)
   Any of a group of three metameric hydrocarbons of the
   aromatic series, found in coal and wood tar, and so named
   because found in crude wood spirit. They are colorless, oily,
   inflammable liquids, {C6H4.(CH3)2}, being dimethyl benzenes,
   and are called respectively {orthoxylene}, {metaxylene}, and
   {paraxylene}. Called also {xylol}.

   Note: Each of these xylenes is the nucleus and prototype of a
         distinct series of compounds.