The Collaborative International Dictionary of English v.0.48:

Commonable \Com"mon*a*ble\, a.
   1. Held in common. "Forests . . . and other commonable
      places." --Bacon.
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   2. Allowed to pasture on public commons.
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            Commonable beasts are either beasts of the plow, or
            such as manure the ground.            --Blackstone.
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