Source : Webster's Revised Unabridged Dictionary (1913)

Renewable \Re*new"a*ble\ (r?-n?"?-b'l), a.
   Capable of being renewed; as, a lease renewable at pleasure.
   --Swift.

Source : WordNet®

renewable
     adj 1: that can be renewed or extended; "a renewable lease";
            "renewable subscriptions" [ant: {unrenewable}]
     2: capable of being renewed; replaceable; "renewable energy
        such as solar energy is theoretically inexhaustible"