WordNet (r) 3.0 (2006):

black magic
    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]

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "black magic":
   Black Mass, Satanism, chthonian worship, demonism, demonography,
   demonolatry, demonology, demonomancy, demonomy, demonry,
   devil lore, devil worship, devilry, diablerie, diabolism,
   diabology, diabolology, sorcery, the black art



The Jargon File (version 4.4.7, 29 Dec 2003):

black magic
 n.

    [common] A technique that works, though nobody really understands why. More
    obscure than voodoo programming, which may be done by cookbook. Compare
    also black art, deep magic, and magic number (sense 2).


The Free On-line Dictionary of Computing (30 December 2018):

black magic

    (Or "FM") A technique that works, though nobody
   really understands why.  More obscure than voodoo
   programming, which may be done by cookbook.

   Compare black art, deep magic, and magic number.

   (2001-04-30)