WordNet (r) 3.0 (2006):

pitch black
    n 1: a very dark black [syn: coal black, ebony, jet black,
         pitch black, sable, soot black]

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "pitch black":
   atramentous, beamless, black, black as coal, black as ebony,
   black as ink, black as midnight, black as night, caliginous,
   coal-black, coaly, dark, dark as night, dark as pitch, darkling,
   darksome, deep black, ebon, ebony, eclipsed, ink-black, inky, jet,
   jetty, midnight, night-black, night-clad, night-cloaked,
   night-dark, night-enshrouded, night-filled, night-mantled,
   night-veiled, nigrous, obfuscated, obscure, obscured, occulted,
   pitch-dark, pitchy, raven, raven-black, rayless, sable, sloe,
   sloe-black, sloe-colored, starless, sunless, tar-black, tarry,
   tenebrious, tenebrose, tenebrous, unilluminated, unlighted,
   unlit