The Collaborative International Dictionary of English v.0.48:

Omniscient \Om*nis"cient\, a. [Omni- + L. sciens, -entis, p. pr.
   of scire to know: cf. F. omniscient. See Science.]
   Having universal knowledge; knowing all things; infinitely
   knowing or wise; as, the omniscient God. --
   Om*nis"cient*ly, adv.
   [1913 Webster]

         For what can scape the eye
         Of God all-seeing, or deceive his heart
         Omniscient?                              --Milton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

omniscient
    adj 1: infinitely wise [syn: all-knowing, omniscient]