The Collaborative International Dictionary of English v.0.48:

Commonage \Com"mon*age\, n. [Cf. OF. communage.]
   The right of pasturing on a common; the right of using
   anything in common with others.
   [1913 Webster]

         The claim of commonage . . . in most of the forests.
                                                  --Burke.
   [1913 Webster]

WordNet (r) 3.0 (2006):

commonage
    n 1: property held in common