unknown
adj
1 not known, understood, or recognized
2 not established, identified, or discovered
an unknown island
3 not famous; undistinguished
some unknown artist
n
4 an unknown person, quantity, or thing
5 (Maths) a variable, or the quantity it represents, the value of which is to be discovered by solving an equation; a variable in a conditional equation
3y = 4x + 5 is an equation in two unknowns
6 ♦
unknown quantity a person or thing whose action, effect, etc., is unknown or unpredictable ♦
unknownness n
Unknown Soldier , Warrior
n (in various countries) an unidentified soldier who has died in battle and for whom a tomb is established as a memorial to other unidentified dead of the nation's armed forces