Webster's Revised Unabridged Dictionary · 1913

Tetramethylene

Tetramethylene , noun

[Tetra- + methylene.]

(a)
(Chemistry) A hypothetical hydrocarbon, C4H8, analogous to trimethylene, and regarded as the base of well-known series or derivatives.
(b)
(Chemistry) Sometimes, an isomeric radical used to designate certain compounds which are really related to butylene.