Source : Webster's Revised Unabridged Dictionary (1913)

Unbelieving \Un`be*liev"ing\, a.
   1. Not believing; incredulous; doubting; distrusting;
      skeptical.

Source : WordNet®

unbelieving
     adj 1: rejecting any belief in gods [syn: {atheistic}, {atheistical}]
     2: holding that only material phenomena can be known and
        knowledge of spiritual matters or ultimate causes is
        impossible [syn: {nescient}]
     3: denying or questioning the tenets of especially a religion;
        "a skeptical approach to the nature of miracles" [syn: {disbelieving},
         {skeptical}, {sceptical}]