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
- unknownness noun
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.
An attorney for Rep. Eric Swalwell, a leading Democratic candidate for California governor, on Thursday sent a cease and desist letter to an unknown individual demanding that they stop accusing the congressman of sexual assault.
From Los Angeles Times • Apr. 10, 2026
Zucker Art Books has the star of the entire fair in its disassembled book by Yuji Itaya, an otherwise unknown amateur lepidopterist who lived in Japan.
From The Wall Street Journal • Apr. 10, 2026
Despite decades of research, its true nature remains unknown.
From Science Daily • Apr. 10, 2026
"Friends," which followed the lives of six New Yorkers navigating adulthood, dating and careers, drew a massive following and made megastars of previously unknown actors.
From Barron's • Apr. 8, 2026
The answers to these questions, like so many others, remained unknown, at least for the moment.
From "The Interrupted Tale" by Maryrose Wood
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.
