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}).
      
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   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}).
         
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   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.
      
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   {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.
      
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White mustard \White mustard\
   A kind of mustard ({Sinapis alba}) with rough-hairy foliage,
   a long-beaked hispid pod, and pale seeds, which yield mustard
   and mustard oil. The plant is also grown for forage.
   [Webster 1913 Suppl.]