The Collaborative International Dictionary of English v.0.48:

Tetramethylene \Tet`ra*meth"yl*ene\, n. [Tetra- + methylene.]
   (Chem.)
   (a) A hypothetical hydrocarbon, C4H8, analogous to
       trimethylene, and regarded as the base of well-known
       series or derivatives.
   (b) Sometimes, an isomeric radical used to designate certain
       compounds which are really related to butylene.
       [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

butene \butene\ n.
   any of three isomeric singly unsaturated hydrocarbons C4H8;
   all are used in making synthetic rubbers; -- called also
   butylene.
   [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Butylene \Bu"ty*lene\, n. [From Butyl.]
   1. (Chem.) Any one of three metameric hydrocarbons, C4H8,
      of the ethylene series. They are gaseous or easily
      liquefiable; -- called also butene.
      [1913 Webster]

   2. the hypothetical divalent radical -(CH2)4-; -- used in
      combining forms; as, butylene diamine.
      [PJC]