What is "crotonylene"

Crotonylene \Cro*ton"y*lene\ (kr?-t?n"?-l?n), n. [Crotonic + acet-ylene.] (Chem.) A colorless, volatile, pungent liquid, C4H6, produced artificially, and regarded as an unsaturated hydrocarbon of the acetylene series, and analogous to crotonic acid.

n. (context organic compound English) A colourless, volatile, pungent liquid, C₄H₆, regarded as an unsaturated hydrocarbon of the acetylene series, analogous to crotonic acid.