The Collaborative International Dictionary of English v.0.48:

Alchemy \Al"che*my\, n. [OF. alkemie, arquemie, F. alchimie, Ar.
   al-k[imac]m[imac]a, fr. late Gr. ?, for ?, a mingling,
   infusion, ? juice, liquid, especially as extracted from
   plants, fr. ? to pour; for chemistry was originally the art
   of extracting the juices from plants for medicinal purposes.
   Cf. Sp. alquimia, It. alchimia. Gr. ? is prob. akin to L.
   fundere to pour, Goth. guitan, AS. ge['o]tan, to pour, and so
   to E. fuse. See Fuse, and cf. Chemistry.]
   1. An imaginary art which aimed to transmute the baser metals
      into gold, to find the panacea, or universal remedy for
      diseases, etc. It led the way to modern chemistry.
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   2. A mixed metal composed mainly of brass, formerly used for
      various utensils; hence, a trumpet. [Obs.]
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            Put to their mouths the sounding alchemy. --Milton.
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   3. Miraculous power of transmuting something common into
      something precious.
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            Kissing with golden face the meadows green,
            Gilding pale streams with heavenly alchemy. --Shak.
      [1913 Webster] Alchymistic
      Alchymist
      Alchymic

WordNet (r) 3.0 (2006):

alchemy
    n 1: the way two individuals relate to each other; "their
         chemistry was wrong from the beginning -- they hated each
         other"; "a mysterious alchemy brought them together" [syn:
         chemistry, interpersonal chemistry, alchemy]
    2: a pseudoscientific forerunner of chemistry in medieval times