unknown
Americanadjective
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not known; not within the range of one's knowledge, experience, or understanding; strange; unfamiliar.
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not discovered, explored, identified, or ascertained.
the unknown parts of Antarctica.
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not widely known; not famous; obscure.
an unknown writer.
noun
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a thing, influence, area, factor, or person that is unknown.
the many unknowns in modern medicine; The director cast an unknown in the leading role.
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Mathematics. a symbol representing an unknown quantity: in algebra, analysis, etc., frequently represented by a letter from the last part of the alphabet, as x, y, or z.
adjective
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not known, understood, or recognized
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not established, identified, or discovered
an unknown island
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not famous; undistinguished
some unknown artist
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a person or thing whose action, effect, etc, is unknown or unpredictable
noun
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an unknown person, quantity, or thing
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maths a variable, or the quantity it represents, the value of which is to be discovered by solving an equation; a variable in a conditional equation
3y = 4x + 5 is an equation in two unknowns
Other Word Forms
Etymology
Origin of unknown
First recorded in 1250–1300, unknown is from the Middle English word unknow(e)n. See un- 1, known
Explanation
If something is unknown, it's not familiar understood, like the unknown path through the woods you've never explored or your brother's unknown reasons for staying late after school. When you're aware ofor familiar with something, you can describe it as known. Add the prefix un-, or "not," and you get unknown. You'll often find this adjective in the phrase "unknown territory," as in "I totally understand algebra, but calculus is unknown territory." And as a noun, the unknown sometimes represents a whole category of mysterious things: "Our fear of the unknown keeps us from traveling to new places."
Vocabulary lists containing unknown
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
Charles and Camilla then visited Arlington National Cemetery just outside Washington, where they laid a wreath and flowers at the hilltop Tomb of the Unknown Soldier honoring America's unidentified war dead.
From Barron's • Apr. 30, 2026
A year after narrowly losing best actor honors with his uncanny Bob Dylan portrayal in "A Complete Unknown," Timothee Chalamet had long appeared a lock for his pushy ping-pong player "Marty Supreme."
From Barron's • Mar. 12, 2026
Note: Unknown outcome refers to unidentified citizens DHS publicly tweeted about.
From The Wall Street Journal • Mar. 8, 2026
Timothée came close to a win last year for playing Bob Dylan in A Complete Unknown, but we're confident that this will be his year to reign supreme.
From BBC • Jan. 22, 2026
She had heard tales of people who tried to go out into the Unknown Regions.
From "The City of Ember" by Jeanne DuPrau
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
