unknown (adj.)

c. 1300, "strange, unfamiliar" (of persons, places), from un- (1) "not" + past participle of know (v.). Compare Old English ungecnawen. In reference to facts, "not discovered or found out," it attested from early 14c. The noun meaning "unknown person" is recorded from 1590s; the unknown "that which is unknown" is from 1650s.

updated on March 23, 2015

Definitions of unknown from WordNet
unknown (adj.)
not known;
an unknown writer
an unknown source
an unknown amount
an unknown island
unknown (adj.)
being or having an unknown or unnamed source;
a poem by an unknown author
unknown (adj.)
not known to exist;
things obscurely felt surged up from unknown depths
unknown (adj.)
not famous or acclaimed;
Synonyms: obscure / unsung
unknown (adj.)
not known before;
don't let anyone unknown into the house
Synonyms: strange
unknown (n.)
an unknown and unexplored region;
they came like angels out the unknown
Synonyms: unknown region / terra incognita
unknown (n.)
anyone who does not belong in the environment in which they are found;
Synonyms: stranger / alien
unknown (n.)
a variable whose values are solutions of an equation;
Synonyms: unknown quantity
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