The Collaborative International Dictionary of English v.0.48:

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).
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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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The Collaborative International Dictionary of English v.0.48:

Treacle \Trea"cle\ (tr[=e]"k'l), n. [OE. triacle a sovereign
   remedy, theriac, OF. triacle, F. th['e]riaque (cf. Pr.
   triacla, tiriaca, Sp. & It. triaca, teriaca), L. theriaca an
   antidote against the bite of poisonous animals, Gr. ?, fr. ?
   of wild or venomous beasts, fr. qhri`on a beast, a wild
   beast, dim. of qh`r a beast. Cf. Theriac.]
   1. (Old Med.) A remedy against poison. See Theriac, 1.
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            We kill the viper, and make treacle of him. --Jer.
                                                  Taylor.
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   2. A sovereign remedy; a cure. [Obs.]
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            Christ which is to every harm treacle. --Chaucer.
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   3. Molasses; sometimes, specifically, the molasses which
      drains from the sugar-refining molds, and which is also
      called sugarhouse molasses.
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   Note: In the United States molasses is the common name; in
         England, treacle.
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   4. A saccharine fluid, consisting of the inspissated juices
      or decoctions of certain vegetables, as the sap of the
      birch, sycamore, and the like.
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   Treacle mustard (Bot.), a name given to several species of
      the cruciferous genus Erysimum, especially the Erysimum
      cheiranthoides, which was formerly used as an ingredient
      in Venice treacle, or theriac.

   Treacle water, a compound cordial prepared in different
      ways from a variety of ingredients, as hartshorn, roots of
      various plants, flowers, juices of plants, wines, etc.,
      distilled or digested with Venice treacle. It was formerly
      regarded as a medicine of great virtue. --Nares.

   Venice treacle. (Old Med.) Same as Theriac, 1.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Erysimum cheiranthoides
    n 1: slender yellow-flowered European mustard often troublesome
         as a weed; formerly used as an anthelmintic [syn: wormseed
         mustard, Erysimum cheiranthoides]