Source : Webster's Revised Unabridged Dictionary (1913)

Conscientiousness \Con`sci*en"tious*ness\, n.
   The quality of being conscientious; a scrupulous regard to
   the dictates of conscience.

Source : WordNet®

conscientiousness
     n 1: the quality of being in accord with the dictates of
          conscience [ant: {unconscientiousness}]
     2: the trait of being painstaking and careful [syn: {painstakingness}]
        [ant: {unconscientiousness}]