What is "sinapism"

Sinapism \Sin"a*pism\, n. [L. sinapismus, Gr. ????, the use of a mustard blister, fr. ??? to apply a mustard blister, fr. ???? 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.

n. Application of a mustard plaster

n. a plaster containing powdered black mustard; applied to the skin as a counterirritant or rubefacient [syn: mustard plaster]