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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unknowns
plural
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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:
Avoid buying devices from unknown individuals, and look closely at the device and packaging, he says.
From The Wall Street Journal ● Aug. 23, 2026
The environmental impact of traditional balloons, which despite their advertising do not degrade, is largely unknown to the general public.
From Barron's ● Aug. 23, 2026
Players have been promised equity under a deal with a new investor, but quite what that equates to remains unknown.
From BBC ● Aug. 21, 2026
The finding adds a previously unknown layer to scientists' understanding of how these medications work.
From Science Daily ● Aug. 20, 2026
But Rania’s voice changes when she switches from talking to her mom to talking to this unknown her.
From "A Rover's Story" by Jasmine Warga
“The fiscal impact of this bill to the courts will depend on many unknowns, including the number of cases filed and the factors unique to each case,” the analysis stated.
From Los Angeles Times ● Aug. 14, 2026
The former has one known factor — your current tax rate — while the latter has two unknowns.
From MarketWatch ● Aug. 6, 2026
Instead, he said, it was a reaction to the refund-related unknowns at the time.
From The Wall Street Journal ● Jul. 23, 2026
But here are a couple of unknowns to watch.
From Slate ● Jul. 11, 2026
Dangerous as they could be to me, somehow, they did not seem as threatening as the dark shadowy woods with its strange sounds, its unknowns.
From "Kindred" by Octavia Butler
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.
