The Collaborative International Dictionary of English v.0.48:

Elixir \E*lix"ir\, n. [F. ['e]lixir, Sp. elixir, Ar.
   eliks[imac]r the philosopher's stone, prob. from Gr. ? dry,
   (hence probably) a dry powder; cf. Skr. ksh[=a] to burn.]
   1. (Med.) A tincture with more than one base; a compound
      tincture or medicine, composed of various substances, held
      in solution by alcohol in some form.
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   2. (Alchemy) An imaginary liquor capable of transmuting
      metals into gold; also, one for producing life
      indefinitely; as, elixir vit[ae], or the elixir of life.
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   3. The refined spirit; the quintessence.
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            The . . . elixir of worldly delights. --South.
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   4. Any cordial or substance which invigorates.
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            The grand elixir, to support the spirits of human
            nature.                               --Addison.
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WordNet (r) 3.0 (2006):

elixir
    n 1: a sweet flavored liquid (usually containing a small amount
         of alcohol) used in compounding medicines to be taken by
         mouth in order to mask an unpleasant taste
    2: hypothetical substance that the alchemists believed to be
       capable of changing base metals into gold [syn:
       philosopher's stone, philosophers' stone, elixir]
    3: a substance believed to cure all ills