Wiktionary
vb. 1 (context transitive English) to undo the process of registration for 2 (context intransitive English) to undo a registration process
Usage examples of "unregister".
Had the authorities missed unregistered disciples who were even now wandering about the Commonwealth, intent on resurrecting that long quiescent, notorious research?
It probably was, he told himself as he coded into the secured room that held his unregistered equipment.
They never spoke about the Ring, or where the unregistered stones came from, or how the finished gems were sent to Switzerland.
However, a day came when there was heard out in the street a very frightening noise of voices, rattling chains, and heavily tramping boots, which brought them to their window, and they saw a company of imperial officers coming to scout out unregistered aliens.