The Collaborative International Dictionary of English v.0.48:

Commonness \Com"mon*ness\, n.
   1. State or quality of being common or usual; as, the
      commonness of sunlight.
      [1913 Webster]

   2. Triteness; meanness.
      [1913 Webster]

WordNet (r) 3.0 (2006):

commonness
    n 1: the state of being that is commonly observed [syn:
         commonness, expectedness]
    2: the quality of lacking taste and refinement [syn:
       coarseness, commonness, grossness, vulgarity,
       vulgarism, raunch]
    3: ordinariness as a consequence of being frequent and
       commonplace [syn: commonness, commonplaceness,
       everydayness] [ant: uncommonness]
    4: sharing of common attributes [syn: commonality,
       commonness] [ant: individualism, individuality,
       individuation]