n.1 a any of various plants of the genus Brassica with slender pods and yellow flowers, esp. B. nigra. b any of various plants of the genus Sinapis, esp. S. alba, eaten at the seedling stage, often with cress.
2 the seeds of these which are crushed, made into a paste, and used as a spicy condiment.
3 the brownish-yellow colour of this condiment.
4 sl. a thing which adds piquancy or zest.
Phrases and idioms:
mustard gas a colourless oily liquid, whose vapour is a powerful irritant and vesicant. mustard plaster a poultice made with mustard. mustard seed 1 the seed of the mustard plant.
2 a small thing capable of great development (Matt. 13:31).
Etymology: ME f. OF mo(u)starde: orig. the condiment as prepared with MUST(2)