Meaning of UNKNOWN in English
[un.known] adj (14c): not known or not well-known; also: having an unknown value "an ~ quantity"
unknown n (1597) 1: one that is not known or not well-known; esp: a person who is little known (as to the public)
2: something that requires discovery, indentification, or clarification: as a: a symbol (as x, y, or z) in a mathematical equation representing an unknown quantity b: a specimen (as of bacteria or mixed chemicals) required to be identified as an exercise in appropriate laboratory techniques
Merriam-Webster English vocab. Английский словарь Merriam Webster. 2012