imprescriptible
Concise Oxford English Dictionary © 2008 Oxford University Press:
imprescriptible /ˌɪmprɪˈskrɪptɪb(ə)l/
▶adjective Law (of rights) unable to be taken away by prescription or by lapse of time.
– origin C16: from med. L. imprescriptibilis.
'imprescriptible' also found in these Oxford entries:

