The Collaborative International Dictionary of English v.0.48:

Justness \Just"ness\, n.
   The quality of being just; conformity to truth, propriety,
   accuracy, exactness, and the like; justice; reasonableness;
   fairness; equity; as, justness of proportions; the justness
   of a description or representation; the justness of a cause.
   [1913 Webster]

         In value the satisfaction I had in seeing it
         represented with all the justness and gracefulness of
         action.                                  --Dryden.
   [1913 Webster]

   Note: Justness is properly applied to things, and justice to
         persons; but the distinction is not always observed.

   Syn: Accuracy; exactness; correctness; propriety; fitness;
        reasonableness; equity; uprightness; justice.
        [1913 Webster]

WordNet (r) 3.0 (2006):

justness
    n 1: conformity with some esthetic standard of correctness or
         propriety; "it was performed with justness and beauty"
         [syn: justness, rightness, nicety]
    2: the quality of being just or fair [syn: justice,
       justness] [ant: injustice, unjustness]