noun
: any of a group of toxic blistering compounds that are analogous in composition to mustard gas but with nitrogen replacing sulfur and that typically are chlorinated tertiary alkylamines ; especially : an amine CH 3 N(CH 2 CH 2 Cl) 2 used in the form of its crystalline hydrochloride in treating neoplastic diseases (as Hodgkin's disease and leukemia); methyl-bis-(2-chloroethyl)-amine