(a) A plant of the genus Brassica; prob. the black mustard (B. nigra) or the white mustard (B. alba), the seeds of which are used in cookery and in medicinal preparations; grain (sed) of ~, ~ sed, a mustard seed; greter ~, ?the black mustard; [some quots. under (a) may belong under (b)]; (b) mustard seed; also, prepared mustard, the finely ground seed of the mustard plant mixed with vinegar, water, or honey to form a paste; also fig.; grete groun ~, ones grind ~, ?coarsely ground mustard seed; ~ gentil, fine mustard [see quot. (?a1400)]; sellen candel and ~, ?to engage in a lowly occupation, ?have to work for one's living; (c) lombard ~ [see quot.Form Cury p.67]; ~ brekers (quernestones), ?stones used to grind mustard seed in a handmill; ~ pot, a container for prepared mustard; ~ presse, ?an apparatus for extracting oil from mustard seed; ~ querne, a handmill for grinding mustard seed; (d) in surnames.