noun 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).
2. mustard ·noun 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.