*sinapism*

n. [ L. sinapismus, Gr. &unr_;&unr_;&unr_;&unr_;, the use of a mustard blister, fr. &unr_;&unr_;&unr_; to apply a mustard blister, fr. &unr_;&unr_;&unr_;&unr_; mustard. ] (Med.) A plaster or poultice composed principally of powdered mustard seed, or containing the volatile oil of mustard seed. It is a powerful irritant. [ 1913 Webster ]