n.
Function: 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