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.
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            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