The Collaborative International Dictionary of English v.0.48:

Medicine \Med"i*cine\, n. [L. medicina (sc. ars), fr. medicinus
   medical, fr. medicus: cf. F. m['e]decine. See Medical.]
   1. The science which relates to the prevention, cure, or
      alleviation of disease.
      [1913 Webster]

   2. Any substance administered in the treatment of disease; a
      remedial agent; a medication; a drug; a pharmaceutical; a
      medicament; a remedy; physic.
      [1913 Webster]

            By medicine, life may be prolonged.   --Shak.
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   3. A philter or love potion. [Obs.] --Shak.
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   4. [F. m['e]decin.] A physician. [Obs.] --Shak.
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   5.
      (a) Among the North American Indians, any object supposed
          to give control over natural or magical forces, to act
          as a protective charm, or to cause healing; also,
          magical power itself; the potency which a charm,
          token, or rite is supposed to exert.
          [Webster 1913 Suppl.]

                The North American Indian boy usually took as
                his medicine the first animal of which he
                dreamed during the long and solitary fast that
                he observed at puberty.           --F. H.
                                                  Giddings.
          [Webster 1913 Suppl.]
      (b) Hence, a similar object or agency among other savages.
          [Webster 1913 Suppl.]

   6. Short for Medicine man.
      [Webster 1913 Suppl.]

   7. Intoxicating liquor; drink. [Slang]
      [Webster 1913 Suppl.]

   Medicine bag, a charm; -- so called among the North
      American Indians, or in works relating to them.

   Medicine man (among the North American Indians), a person
      who professes to cure sickness, drive away evil spirits,
      and regulate the weather by the arts of magic; a shaman.


   Medicine seal, a small gem or paste engraved with reversed
      characters, to serve as a seal. Such seals were used by
      Roman physicians to stamp the names of their medicines.
      [1913 Webster]

WordNet (r) 3.0 (2006):

medicine man
    n 1: a Native American shaman

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "medicine man":
   charlatan, exorciser, exorcist, horse doctor, medicaster,
   medicine monger, mundunugu, obeah doctor, quack, quacksalver,
   shaman, shamanist, unspeller, voodoo, voodooist, wangateur,
   witch doctor, witch master, witch-finder, witchman