from The American Heritage® Dictionary of the English Language, 5th Edition.

  • adjective Not known; unfamiliar.
  • adjective Not identified, ascertained, or established.
  • adjective Not well known or widely known.
  • noun That which is unknown.
  • noun Something that is not known.
  • noun A person who is not well known, as to the general public.
  • noun An unknown person, especially an Unknown Soldier.
  • noun Mathematics A quantity of unknown numerical value.

from The Century Dictionary.

  • Not known; not become an object of knowledge; not recognized, discovered, or found out.
  • Unknown in this sense is often used in the predicate, followed by to: as, a man unknown to fame; a fact unknown to the public. In this use it is also often used absolntely: as, unknown to me (elliptically for it being unknown to me), he made a new contract.
  • Not ascertained, with relation to extent, degree, quantity, or the like; hence, incalculable; inexpressible; immense.
  • Not to be made known, expressed, or communicated.
  • Not having had sexual commerce.
  • noun One who or that which is unknown.

from the GNU version of the Collaborative International Dictionary of English.

  • adjective Not known; not apprehended.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • adjective Not known; unidentified; not well known.
  • noun algebra A variable (usually x, y or z) whose value is to be found.
  • noun Any fact or place about which nothing is known (as in the phrase "into the unknown").
  • noun A person of no identity; a nonentity

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • adjective not famous or acclaimed
  • adjective not known before
  • noun an unknown and unexplored region
  • noun a variable whose values are solutions of an equation
  • adjective not known to exist
  • adjective not known
  • adjective being or having an unknown or unnamed source
  • noun anyone who does not belong in the environment in which they are found


from Wiktionary, Creative Commons Attribution/Share-Alike License

From un- +‎ known, past participle of know. Cf. Old English ungecnawen.



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  • "There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don't know. But there are also unknown unknowns. There are things we don't know we don't know."

    - Donald Rumsfeld.

    July 24, 2009

  • I think the opening lines of this song say it all.

    July 24, 2009

  • I think that we whould leave some known unknowns as they are (mostly concerning space).

    Also, are there things that we don't know we know? Is it possible?

    July 24, 2009