from The American Heritage® Dictionary of the English Language, 4th Edition

  • adj. Not known; unfamiliar: a modern-day problem unknown in earlier times.
  • adj. Not identified or ascertained: received flowers from an unknown admirer.
  • adj. Not established or verified.
  • adj. Not well known or widely known: an unknown artist.
  • n. A person or thing that is unknown: "the abyss of the unknown” ( Helena Petrovna Blavatsky).
  • n. A person who is not well known, as to the general public: cast an unknown in the starring role.
  • n. Mathematics A quantity of unknown numerical value.

from Wiktionary, Creative Commons Attribution/Share-Alike License

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

from the GNU version of the Collaborative International Dictionary of English

  • adj. Not known; not apprehended.

from The Century Dictionary and Cyclopedia

  • 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.
  • n. One who or that which is unknown.

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

  • adj. not famous or acclaimed
  • adj. not known before
  • n. an unknown and unexplored region
  • n. a variable whose values are solutions of an equation
  • adj. not known to exist
  • adj. not known
  • adj. being or having an unknown or unnamed source
  • n. 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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  • 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

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

    July 24, 2009

  • "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