Source : Webster's Revised Unabridged Dictionary (1913)

Convexity \Con*vex"i*ty\, n.; pl. {Convexities}. [L. convexitas:
   cf. F. convexit['e].]
   The state of being convex; the exterior surface of a convex
   body; roundness.

         A smooth, uniform convexity and rotundity of a globe.
                                                  --Bentley.

Source : WordNet®

convexity
     n 1: the property possessed by a convex shape [syn: {convexness}]
     2: a shape that curves or bulges outward [syn: {convex shape}]