Source : Webster's Revised Unabridged Dictionary (1913)

Unknown \Un*known"\, a.
   Not known; not apprehended. -- {Un*known"ness}, n. [R.]
   --Camden.

Source : WordNet®

unknown
     adj 1: not known; "an unknown amount"; "an unknown island"; "an
            unknown writer"; "an unknown source" [ant: {known}]
     2: being or having an unknown or unnamed source; "a poem by an
        unknown author"; "corporations responsible to nameless
        owners"; "an unnamed donor" [syn: {nameless}, {unidentified},
         {unnamed}]
     3: not known to exist; "things obscurely felt surged up from
        unsuspected depths in her"- Edith Wharton
     4: not famous or acclaimed; "an obscure family"; "unsung heroes
        of the war" [syn: {obscure}, {unsung}]
     5: not known before; "used many strange words"; "saw many
        strange faces in the crowd"; "don't let anyone unknown
        into the house" [syn: {strange}]
     n 1: an unknown and unexplored region; "they came like angels out
          the unknown" [syn: {unknown region}, {terra incognita}]
     2: anyone who does not belong in the environment in which they
        are found [syn: {stranger}, {alien}]
     3: a variable whose values are solutions of an equation [syn: {unknown
        quantity}]