hexene

from The Collaborative International Dictionary of English v.0.48

Hexylene \Hex"yl*ene\, n. [Hex- + -yl + ethlene.] (Chem.)
   A colorless, liquid hydrocarbon, {C6H12}, of the ethylene
   series, produced artificially, and found as a natural product
   of distillation of certain coals; also, any one several
   isomers of hexylene proper. Called also {hexene}.
   [1913 Webster]

from The Collaborative International Dictionary of English v.0.48

Hexene \Hex"ene\, n. [Gr. "e`x six.] (Chem.)
   Same as {Hexylene}.
   [1913 Webster]