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
Derived Forms
Inflected Forms
Nouns
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.
See Examples For:
Whether Jefferson had any knowledge or opinion of Hamilton’s fondness for Laurens is unknown.
From Salon ● Jul. 27, 2026
Kristine Garroway, a longtime member with an archeological background, told The Times last year that the previous mural dated to the 1920s, although its true origin remains unknown.
From Los Angeles Times ● Jul. 25, 2026
"The whereabouts of eight people is unknown and rescue operations are ongoing," said Yevgeny Balitsky, the Kremlin-installed head of the Russian-occupied part of the Zaporizhzhia region.
From Barron's ● Jul. 25, 2026
Armed with stolen credentials of unknown origin, the AI interloper popped up a “swarm” of short-lived attackers that conducted reconnaissance of the Hugging Face network.
From The Wall Street Journal ● Jul. 24, 2026
That would take him out of the small patch of the Forest that he knew, and into the unknown.
From "Wolf Brother" by Michelle Paver
But here are a couple of unknowns to watch.
From Slate ● Jul. 11, 2026
Tournament success requires adaptability to deal with unknowns.
From BBC ● Jul. 6, 2026
When “The Traitors” executive producer Mike Cotton and his colleagues brought the first season of Peacock’s reality competition to American audiences, doing so with a cast of unknowns scheming for a six-figure prize seemed risky.
From Los Angeles Times ● Jun. 8, 2026
But the known unknowns are enough to keep the election interesting.
From The Wall Street Journal ● Jun. 3, 2026
It was as if because of their train meeting years ago, they could bypass several steps, ignore several unknowns, and slide into an immediate intimacy.
From "Americanah" by Chimamanda Ngozi Adichie
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.
