\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.