Source : Webster's Revised Unabridged Dictionary (1913)

Gnostic \Gnos"tic\, a.
   1. Knowing; wise; shrewd. [Old Slang]

            I said you were a gnostic fellow.     --Sir W.
                                                  Scott.

   2. (Eccl. Hist.) Of or pertaining to Gnosticism or its
      adherents; as, the Gnostic heresy.

Gnostic \Gnos"tic\, n. [L. gnosticus, Gr. ? good at knowing,
   sagacious; as a n., man that claims to have a deeper wisdom,
   fr. gignw`skein to know: cf. F. gnostique. See {Know}.]
   (Eccl. Hist.)
   One of the so-called philosophers in the first ages of
   Christianity, who claimed a true philosophical interpretation
   of the Christian religion. Their system combined Oriental
   theology and Greek philosophy with the doctrines of
   Christianity. They held that all natures, intelligible,
   intellectual, and material, are derived from the Deity by
   successive emanations, which they called Eons.

Source : WordNet®

Gnostic
     adj 1: of or relating to Gnosticism; "Gnostic writings"
     2: possessing intellectual or esoteric knowledge of spiritual
        things [ant: {agnostic}]

Gnostic
     n : an advocate of gnosticism