Meaning of UNKNOWN in English

UNKNOWN

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.