simple past tense and past participle of unregister
"The unregistered voters were allowed to cast their ballots after providing proof of identity at the polling station."
In plain English: To unregister means to officially remove your name from a list so you are no longer counted as part of that group or system.
"The driver received a fine for unregistering his vehicle before taking it off the road."
(of animals) not recorded with or certified by an official breed association
"unregistered dairy cattle"
(a boat or vessel) not furnished with official documents
"The unregistered fishing boat was stopped by customs officers because it lacked any official documentation."
Not registered.
"The unregistered vehicle was unable to pass through the border checkpoint because it lacked valid plates."
The word unregistered is formed by adding the prefix un- to registered. This straightforward construction indicates that something has not been officially recorded or enrolled.