The Collaborative International Dictionary of English v.0.48:

Decoction \De*coc"tion\, n. [F. d['e]coction, L. decoctio.]
   1. The act or process of boiling anything in a watery fluid
      to extract its virtues.
      [1913 Webster]

            In decoction . . . it either purgeth at the top or
            settleth at the bottom.               --Bacon.
      [1913 Webster]

   2. An extract got from a body by boiling it in water.
      [1913 Webster]

            If the plant be boiled in water, the strained liquor
            is called the decoction of the plant. --Arbuthnot.
      [1913 Webster]

            In pharmacy decoction is opposed to infusion, where
            there is merely steeping.             --Latham.
      [1913 Webster]

WordNet (r) 3.0 (2006):

decoction
    n 1: (pharmacology) the extraction of water-soluble drug
         substances by boiling

Moby Thesaurus II by Grady Ward, 1.0:

55 Moby Thesaurus words for "decoction":
   boil, boiling, brew, chemical solution, coction, combination,
   composition, concentrate, concentration, concoction, confection,
   decoctum, distillate, distillation, ebullience, ebulliency,
   ebulliometer, ebullition, elixir, essence, expression, extract,
   extraction, imbuement, impregnation, infiltration, infusion,
   instillation, instillment, interpenetration, leach, leachate,
   lixivium, marination, mixture, penetration, permeation, pervasion,
   pressing, purification, quintessence, refinement, rendering,
   rendition, saturation, seething, simmer, simmering, soaking,
   solution, spirit, squeezing, steeping, stewing, suffusion



Bouvier's Law Dictionary, Revised 6th Ed (1856):

DECOCTION, med. jurisp. The operation of boiling certain ingredients in a
fluid, for the purpose of extracting the parts soluble at that temperature.
Decoction also means the product of this operation.
     2. In a case in which the indictment charged the prisoner with having
administered to a woman a decoction of a certain shrub called savin, it
appeared that the prisoner had administered an infusion (q.v.) and not a
decoction; the prisoner's counsel insisted that he was entitled to an
acquittal, on the ground that the medicine was misdescribed, but it was held
that infusion and decoction are ejusdem generis, and that the variance was
immaterial. 3 Camp. R. 74, 75.