Webster’s Revised Unabridged Dictionary · 1913
Sinapism
Sin′a·pism, n. [L. sinapismus, Gr. σιναπισμός, the use of a mustard blister, fr. σιναπίζειν to apply a mustard blister, fr. σίναπι 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.