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]

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "incognizant":
   a stranger to, asleep, blind to, caught napping, dead to, deaf to,
   impercipient, in ignorance of, insensible, insensible to, mindless,
   napping, nonconceiving, not with it, oblivious, out of it, unaware,
   unaware of, unconscious, unconscious of, unhearing, uninsightful,
   unknowing, unmindful, unmindful of, unperceiving, unprehensive,
   unrealizing, unseeing, unsuspecting, unwitting, witless