The Collaborative International Dictionary of English v.0.48:

Imprescriptible \Im`pre*scrip"ti*ble\, a. [Pref. im- not +
   prescriptible: cf. F. imprescriptible.]
   1. Not capable of being lost or impaired by neglect, by
      disuse, or by the claims of another founded on
      prescription; -- of rights.
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            The right of navigation, fishing, and others that
            may be exercised on the sea, belonging to the right
            of mere ability, are imprescriptible. --Vattel
                                                  (Trans. )
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   2. Not derived from, or dependent on, external authority;
      self-evidencing; obvious.
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            The imprescriptible laws of the pure reason.
                                                  --Colerridge.
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