The Collaborative International Dictionary of English v.0.48:

Theriac \The"ri*ac\, Theriaca \The*ri"a*ca\, n. [L. theriaca an
   antidote against the bite of serpents, Gr. ?: cf. F.
   th['e]riaque. See Treacle.]
   1. (Old Med.) An ancient composition esteemed efficacious
      against the effects of poison; especially, a certain
      compound of sixty-four drugs, prepared, pulverized, and
      reduced by means of honey to an electuary; -- called also
      theriaca Andromachi, and Venice treacle.
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   2. Treacle; molasses. --British Pharm.
      [1913 Webster] Theriac

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.
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