Source : Webster's Revised Unabridged Dictionary (1913)

Roundness \Round"ness\, n.
   1. The quality or state of being round in shape; as, the
      roundness of the globe, of the orb of the sun, of a ball,
      of a bowl, a column, etc.

   2. Fullness; smoothness of flow; as, the roundness of a
      period; the roundness of a note; roundness of tone.

   3. Openess; plainess; boldness; positiveness; as, the
      roundness of an assertion.

   Syn: Circularity; sphericity; globosity; globularity;
        globularness; orbicularness; cylindricity; fullness;
        plumpness; rotundity.

Source : WordNet®

roundness
     n : the property possessed by a line or surface that is curved
         and not angular [ant: {angularity}]