un·known 
(ŭn-nōn)
(ŭn-nōn)adj.
1. Not known; unfamiliar: a problem unknown in earlier times.
2. Not identified, ascertained, or established: received flowers from an unknown admirer.
3. Not well known or widely known: an unknown artist.
n.
1.
a. That which is unknown: investigating the unknown.
b. Something that is not known: This case has many unknowns.
c. A person who is not well known, as to the general public: cast an unknown in the starring role.
d. An unknown person, especially an Unknown Soldier: the tomb of the unknowns.
2. Mathematics A quantity of unknown numerical value.