*imprescriptib*

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. [ 1913 Webster ]

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. ) [ 1913 Webster ]

2. Not derived from, or dependent on, external authority; self-evidencing; obvious. [ 1913 Webster ]

The imprescriptible laws of the pure reason. Colerridge. [ 1913 Webster ]