Mustard plaster

Mustard plaster: A mild mixture of mustard seed powder, an adhesive such as flour, and water warmed and spread on a moist cloth that is then applied to the skin. The original mistaken notion was that the mustard plaster would draw out the "bad humors." It acts as a counterirritant and increases the local blood supply. a mustard plaster is a form of poultice. See also: Cataplasm.