The Collaborative International Dictionary of English v.0.48:

Incognizant \In*cog"ni*zant\, a.
   Not cognizant; failing to apprehended or notice.
   [1913 Webster]

         Of the several operations themselves, as acts of
         volition, we are wholly incognizant.     --Sir W.
                                                  Hamilton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

incognizant
    adj 1: (often followed by `of') not aware; "seemed unaware of
           the scrutiny"; "unaware of the danger they were in";
           "unaware of the newborn hope"; "the most unaware person
           I've known" [syn: unaware, incognizant] [ant:
           aware(p), cognisant, cognizant]