un‧known 1 W2 / ʌnnəʊn◂ $ -noʊn◂ / 形容词 , 副词

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