unknown
un‧known1 W2 /ˌʌnˈnəʊn◂ $ -ˈnoʊn◂/ 
adjective, adverb
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
unknown2 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
| I |
adjective, adverb Word Family: adjective: knowing, knowledgeable, known ≠ unknown; noun: knowledge, the unknown; adverb: knowingly ≠ unknowingly, knowledgeably; verb: know
1. not known about: 2. not famous:
3. unknown to somebody without someone knowing:
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 |
noun [countable]1. someone who is not famous:
2. something that is not known:
3. the unknown
a. a place that is not known about or that has not been visited by humans:
b. things that you do not know or understand: