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