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.
- put foot in one's mouth
- put forth
- put forward
- put/have all (one's) eggs in one basket
- put heads together
- put house in order
- put in
- Putin
- put in an appearance
- Put-in-Bay
- put in mind
- put in place
- put in someone's place
- put in work
- put it all together
- put it to
- put it to (someone)
- put it to someone
- put/lay (one's) cards on the table
- putlog
- put money on
- put money where mouth is
- put money where one's mouth is
- Putnam
- Putnam