From WordNet (r) 3.0 (2006) [wn]:
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,
unknown, unnamed]
3: not known to exist; "things obscurely felt surged up from
unknown depths"
4: not famous or acclaimed; "an obscure family"; "unsung heroes
of the war" [syn: obscure, unknown, 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, unknown]
n 1: an unknown and unexplored region; "they came like angels
out the unknown" [syn: unknown, unknown region, {terra
incognita}]
2: anyone who does not belong in the environment in which they
are found [syn: stranger, alien, unknown] [ant:
acquaintance, friend]
3: a variable whose values are solutions of an equation [syn:
unknown, unknown quantity]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Unknown \Un*known"\, a.
Not known; not apprehended. -- Un*known"ness, n. [R.]
--Camden.
[1913 Webster]