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