a pungent powder or paste prepared from the seed of the mustard plant, used as a food seasoning or condiment, and medicinally in plasters, poultices, etc.

any of various acrid or pungent plants, esp. of the genus Brassica, as B. juncea (leaf mustard), the leaves of which are used for food and B. nigra (black mustard), the chief source of commercial mustard, and Sinapis alba (white mustard). Compare mustard family .

nitrogen mustard. ?

cut the mustard

Slang . to reach or surpass the desired standard of performance

a pitcher who cuts the mustard with his fastball.