The Collaborative International Dictionary of English v.0.48:

Necromancy \Nec"ro*man`cy\, n. [OE. nigromaunce, nigromancie,
   OF. nigromance, F. n['e]cromance, n['e]cromancie, from L.
   necromantia, Gr. ?; nekro`s a dead body (akin to L. necare to
   kill, Skr. na[,c] to perish, vanish) + ? divination, fr. ?
   diviner, seer, akin to E. mania. See Mania, and cf.
   Internecine, Noxious. The old spelling is due to
   confusion with L. niger black. Hence the name black art.]
   The art of revealing future events by means of a pretended
   communication with the dead; the black art; hence, magic in
   general; conjuration; enchantment. See Black art.
   [1913 Webster]

         This palace standeth in the air,
         By necromancy plac[`e]d there.           --Drayton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

necromancy
    n 1: the belief in magical spells that harness occult forces or
         evil spirits to produce unnatural effects in the world
         [syn: sorcery, black magic, black art, necromancy]
    2: conjuring up the dead, especially for prophesying

Moby Thesaurus II by Grady Ward, 1.0:

43 Moby Thesaurus words for "necromancy":
   alchemy, bewitchery, bewitchment, charm, divination, enchantment,
   fetishism, glamour, gramarye, hoodoo, juju, jujuism, magic,
   mediumism, natural magic, obeah, rune, seance, shamanism, sitting,
   sorcery, sortilege, spell, spellbinding, spellcasting, spirit,
   spiritism, spiritualism, sympathetic magic, thaumaturgia,
   thaumaturgics, thaumaturgism, thaumaturgy, theurgy, vampirism,
   voodoo, voodooism, wanga, white magic, witchcraft, witchery,
   witchwork, wizardry