The Collaborative International Dictionary of English v.0.48:

Rotundity \Ro*tund"i*ty\, n. [L. rotunditas: cf. F.
   rotondit['e].]
   1. The state or quality of being rotu?; roundness;
      sphericity; circularity.
      [1913 Webster]

            Smite flat the thick rotundity o'the world! --Shak.
      [1913 Webster]

   2. Hence, completeness; entirety; roundness.
      [1913 Webster]

            For the more rotundity of the number and grace of
            the matter, it passeth for a full thousand.
                                                  --Fuller.
      [1913 Webster]

            A boldness and rotundity of speech.   --Hawthorne.
      [1913 Webster]

WordNet (r) 3.0 (2006):

rotundity
    n 1: the roundness of a 3-dimensional object [syn: sphericity,
         sphericalness, globosity, globularness, rotundity,
         rotundness]
    2: the fullness of a tone of voice; "there is a musky roundness
       to his wordiness" [syn: roundness, rotundity]