The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

         A smooth, uniform convexity and rotundity of a globe.
                                                  --Bentley.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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

Moby Thesaurus II by Grady Ward, 1.0:

82 Moby Thesaurus words for "convexity":
   aduncity, aquilinity, arching, arcuation, belly, boss, bump,
   circularity, colophon, concameration, concavity, convolution,
   crookedness, curvation, curvature, curving, curvity,
   cylindricality, dactylogram, dactylograph, decurvation,
   decurvature, dent, dint, embossment, excrescence, excurvation,
   excurvature, fingerprint, footmark, footprint, footstep,
   fossil footprint, globosity, globularity, hookedness, ichnite,
   ichnolite, impress, impression, imprint, incurvation, incurvature,
   incurvity, indent, indentation, indention, lump, orbicularity, pad,
   paw print, pawmark, pimple, print, pug, pugmark, recurvation,
   recurvature, recurvity, rondure, rotundity, rotundness, roundness,
   seal, sigil, signet, sinuosity, sinuousness, sphericality,
   sphericalness, sphericity, spheroidicity, spheroidity, stamp, step,
   stud, thumbmark, thumbprint, tortuosity, tortuousness, vaulting,
   vestige