Source : Webster's Revised Unabridged Dictionary (1913)

Incognizant \In*cog"ni*zant\, a.
   Not cognizant; failing to apprehended or notice.

         Of the several operations themselves, as acts of
         volition, we are wholly incognizant.     --Sir W.
                                                  Hamilton.

Source : WordNet®

incognizant
     adj : (often followed by `of') lacking knowledge or awareness;
           "incognizant of the new political situation" [syn: {unaware}]
           [ant: {cognizant}]