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.
      [1913 Webster]

   2. A mixed metal composed mainly of brass, formerly used for
      various utensils; hence, a trumpet. [Obs.]
      [1913 Webster]

            Put to their mouths the sounding alchemy. --Milton.
      [1913 Webster]

   3. Miraculous power of transmuting something common into
      something precious.
      [1913 Webster]

            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

Moby Thesaurus II by Grady Ward, 1.0:

62 Moby Thesaurus words for "alchemy":
   about-face, assimilation, assumption, becoming, bewitchery, change,
   change-over, charm, conversion, divination, enchantment, fetishism,
   flip-flop, glamour, gramarye, growth, hoodoo, juju, jujuism, lapse,
   magic, natural magic, naturalization, necromancy, obeah, passage,
   progress, re-formation, reconversion, reduction, resolution,
   reversal, rune, shamanism, shift, sorcery, sortilege, spell,
   spellbinding, spellcasting, switch, switch-over, sympathetic magic,
   thaumaturgia, thaumaturgics, thaumaturgism, thaumaturgy, theurgy,
   transformation, transit, transition, turning into, vampirism,
   volte-face, voodoo, voodooism, wanga, white magic, witchcraft,
   witchery, witchwork, wizardry