Webster's Revised Unabridged Dictionary · 1913

Isoprene

Isoprene , noun

[Etymol. uncertain.]

(Chemistry) An oily, volatile unsaturated hydrocarbon (C5H8), obtained by the distillation of caoutchouc or gutta-percha, and used to make synthetic rubber by polymerization. In organic chemistry, it is viewed conceptually as the building block of the terpene series of hydrocarbons.