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]