The Collaborative International Dictionary of English v.0.48:

Omniscience \Om*nis"cience\, n. [Cf. F. omniscience.]
   The quality or state of being omniscient; the quality of
   knowing everything; -- an attribute peculiar to God.
   --Dryden.
   [1913 Webster]

WordNet (r) 3.0 (2006):

omniscience
    n 1: the state of being omniscient; having infinite knowledge

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "omniscience":
   all-knowingness, cross-disciplinary knowledge, deep knowledge,
   encyclopedic knowledge, eternity, expertise, extensive knowledge,
   general knowledge, glory, holiness, immutability,
   infinite goodness, infinite justice, infinite love, infinite mercy,
   infinite power, infinite wisdom, infinity, light, majesty,
   omnipotence, omnipotency, omnipresence, omnisciency, pansophy,
   polyhistory, polymathy, proficiency, profound knowledge,
   sovereignty, special knowledge, ubiquity, unity