I. -ˈnōn adjective
Date: 14th century
: not known or not well-known ; also : having an unknown value
an unknown quantity
II. noun
Date: 1597
1. : one that is not known or not well-known ; especially : a person who is little known (as to the public)
2. : something that requires discovery, identification, 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