unknown
un-known
adjective
Not known or identified; unfamiliar or mysterious to someone.
"The cause of the fire remains unknown."
noun
An unknown person, thing, or quantity; something not yet discovered.
"They ventured into the great unknown."
Thesaurus
Synonyms: unsuspected, terra incognita, unknown region, anon., anonymous, unnamed, unidentified, nameless, unfamiliar, strange, unsung, inglorious
Antonyms: acquaintance, friend, known