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.
      [1913 Webster]

   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.
      [1913 Webster]

   3. The refined spirit; the quintessence.
      [1913 Webster]

            The . . . elixir of worldly delights. --South.
      [1913 Webster]

   4. Any cordial or substance which invigorates.
      [1913 Webster]

            The grand elixir, to support the spirits of human
            nature.                               --Addison.
      [1913 Webster]

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

Moby Thesaurus II by Grady Ward, 1.0:

99 Moby Thesaurus words for "elixir":
   axiom, balm, balsam, base, basis, broad-spectrum drug, catholicon,
   center, compound, concentrate, concentration, core, cure, cure-all,
   decoction, distillate, distillation, drops, drug, electuary,
   elixir of life, elixir vitae, essence, essential, ethical drug,
   extract, extraction, fabric, flower, focus, fundamental,
   generic name, gist, gravamen, heart, herbs, hypostasis, infusion,
   inhalant, inner essence, kernel, lincture, linctus, marrow,
   materia medica, material, matter, meat, medicament, medication,
   medicinal, medicinal herbs, medicine, medium, mixture,
   nonprescription drug, nostrum, nub, nucleus, nuts and bolts,
   officinal, panacea, patent medicine, pharmacon, physic, pith,
   polychrest, postulate, potion, powder, preparation,
   prescription drug, principle, proprietary, proprietary medicine,
   proprietary name, purification, quid, quiddity, quintessence,
   refinement, sap, simples, soul, sovereign remedy, spirit, stuff,
   substance, sum and substance, syrup, the nitty-gritty, therapeutic,
   theraputant, therapy, theriac, tincture, tisane, universal remedy,
   vegetable remedies