noun
Etymology: so called from its odor
: a vesicant war gas (ClCH 2 CH 2 ) 2 S that also attacks the eyes and lungs and is a systemic poison, that is a high-boiling oily liquid with a pungent odor only when impure, and that is obtained by treating thiodiglycol with gaseous hydrogen chloride or ethylene with sulfur monochloride; bis-(2-chloroethyl) sulfide — called also dichloroethyl sulfide, sulfur mustard