B1
not known or familiar
Dictionary examples:
The unknown location of my keys is a daily mystery. (0.0)
The source of the mysterious laughing in the library remains unknown. (0.0)
The unknown reason why my plants die is probably my singing. (0.0)
The exact number of people carrying the virus is unknown. (31.3)
As recently as six months ago her name was unknown to most Americans. (35.4)