C6H4(CH3)2

from The Collaborative International Dictionary of English v.0.48

Orthoxylene \Or`tho*xy"lene\, n. [Ortho- + xylene.] (Chem.)
   That variety of xylene ({C6H4(CH3)2}) in which the two methyl
   groups are in the ortho position; a colorless, liquid,
   combustible hydrocarbon resembling benzene.
   [1913 Webster]

from The Collaborative International Dictionary of English v.0.48

Paraxylene \Par`a*xy"lene\, n. (Chem.)
   A hydrocarbon ({C6H4(CH3)2}) of the aromatic series obtained
   as a colorless liquid by the distillation of camphor with
   zinc chloride. It is one of the three metamers of xylene. Cf.
   {Metamer}, and {Xylene}.
   [1913 Webster]

from The Collaborative International Dictionary of English v.0.48

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}.
   [1913 Webster]

   Note: Each of these xylenes is the nucleus and prototype of a
         distinct series of compounds.
         [1913 Webster]