Source : Webster's Revised Unabridged Dictionary (1913)

Clearness \Clear"ness\, n.
   The quality or state of being clear.

   Syn: {Clearness}, {Perspicuity}.

   Usage: Clearness has reference to our ideas, and springs from
          a distinct conception of the subject under
          consideration. Perspicuity has reference to the mode
          of expressing our ideas and belongs essentially to
          style. Hence we speak of a writer as having clear
          ideas, a clear arrangement, and perspicuous
          phraseology. We do at times speak of a person's having
          great clearness of style; but in such cases we are
          usually thinking of the clearness of his ideas as
          manifested in language. ``Whenever men think clearly,
          and are thoroughly interested, they express themselves
          with perspicuity and force.'' --Robertson.

Source : WordNet®

clearness
     n 1: free from obscurity and easy to understand; the
          comprehensibility of clear expression [syn: {clarity}, {lucidity},
           {pellucidity}, {limpidity}] [ant: {unclearness}, {obscureness}]
     2: the quality of clear water; "when she awoke the clarity was
        back in her eyes" [syn: {clarity}, {uncloudedness}] [ant:
        {opacity}]