The Collaborative International Dictionary of English v.0.48:

Necromancer \Nec"ro*man`cer\, n.
   One who practices necromancy; a sorcerer; a wizard.
   [1913 Webster]

WordNet (r) 3.0 (2006):

necromancer
    n 1: one who practices magic or sorcery [syn: sorcerer,
         magician, wizard, necromancer, thaumaturge,
         thaumaturgist]
    2: one who practices divination by conjuring up the dead

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "necromancer":
   Comus, Faust, automatist, charmer, conjurer, diabolist, diviner,
   dowser, ecstatic, enchanter, mage, magus, medium, miracle-worker,
   psychic, psychographist, sorcerer, spirit rapper, spiritist,
   spiritualist, thaumaturge, thaumaturgist, theurgist, voodooist,
   warlock, water witch, wizard



Easton's 1897 Bible Dictionary:

Necromancer
   (Deut. 15:11), i.e., "one who interrogates the dead," as the
   word literally means, with the view of discovering the secrets
   of futurity (comp. 1 Sam. 28:7). (See DIVINATION.)