Meaning of UNKNOWN in English
I. un ‧ known 1 W2 /ˌʌnˈnəʊn◂ $ -ˈnoʊn◂/ BrE AmE adjective , adverb
[ Word Family: adjective : ↑ knowing , ↑ knowledgeable , ↑ known ≠ ↑ unknown ; noun : ↑ knowledge , the unknown; adverb : ↑ knowingly ≠ ↑ unknowingly , ↑ knowledgeably ; verb : ↑ know ]
1 . not known about:
The murderer’s identity remains unknown.
For some unknown reason, Mark quit his job and moved to Greece.
a voyage through unknown territory
An unknown number of people were killed.
2 . not famous:
an unknown artist
3 . unknown to somebody without someone knowing:
Unknown to his wife, Ron had been having an affair.
4 . be an unknown quantity if someone or something is an unknown quantity, you do not know what their abilities are or how they are likely to behave
II. unknown 2 BrE AmE noun [countable]
1 . someone who is not famous:
At that point in her career she was still an unknown.
2 . something that is not known:
The long-term effects of the drug are still an unknown.
3 . the unknown
a) a place that is not known about or that has not been visited by humans:
The astronauts began their journey into the unknown.
b) things that you do not know or understand:
a fear of the unknown
Longman Dictionary of Contemporary English. Longman - Словарь современного английского языка. 2012