Arabis perfoliata

Mustard Mus"tard, n. [OF. moustarde, F. moutarde, fr. L. mustum must, -- mustard was prepared for use by being mixed with must. See {Must}, n.] 1. (Bot.) The name of several cruciferous plants of the genus {Brassica} (formerly {Sinapis}), as {white mustard} ({Brassica alba}), {black mustard} ({Brassica Nigra}), {wild mustard} or {charlock} ({Brassica Sinapistrum}). [1913 Webster]

Note: There are also many herbs of the same family which are called mustard, and have more or less of the flavor of the true mustard; as, bowyer's mustard ({Lepidium ruderale}); hedge mustard ({Sisymbrium officinale}); Mithridate mustard ({Thlaspi arvense}); tower mustard ({Arabis perfoliata}); treacle mustard ({Erysimum cheiranthoides}). [1913 Webster]

2. 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. [1913 Webster]

{Mustard oil} (Chem.), a substance obtained from mustard, as a transparent, volatile and intensely pungent oil. The name is also extended to a number of analogous compounds produced either naturally or artificially. [1913 Webster]