Definition of mustard

• n. - The name of several cruciferous plants of the genus Brassica (formerly Sinapis), as white mustard (B. alba), black mustard (B. Nigra), wild mustard or charlock (B. Sinapistrum).
• n. - A powder or a paste made from the seeds of black or white mustard, used as a condiment and a rubefacient. Taken internally it is stimulant and diuretic, and in large doses is emetic.