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:
An impatience with the notion of impossibility, chafing at all boundaries and limits, straining to peer into the depths of the unknown.
From The Wall Street Journal ● Oct. 8, 2026
Although the quarry was discovered in 1992 and excavated through 2019, many of the fossils recovered there had never been formally described and remained largely unknown to science.
From Science Daily ● Oct. 8, 2026
Thousands of people – including an unknown number of outside troublemakers – have been arrested.
From BBC ● Oct. 8, 2026
I am uncomfortable with this arrangement because so much is unknown.
From MarketWatch ● Oct. 6, 2026
For unknown reasons, there are some who have little or no protection.
From "At Last She Stood" by Erin Entrada Kelly
There are any number of unknowns, but one thing is clear: A majority of the justices ruled that mifepristone access should remain unchanged during litigation in the case.
From Slate ● Sep. 16, 2026
Recent warnings about the potential dangers of AI show that there are significant unknowns with such a rapid growth of a new industry.
From BBC ● Sep. 15, 2026
“For us to take that risk and gamble with a new factory, tariff unknowns, shipping unknowns—at this point, we are deciding that it’s just not a risk that we’re willing to take,” she said.
From The Wall Street Journal ● Sep. 1, 2026
“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
If we were to stop asking questions, then how would we ever uncover the unknowns of the universe?
From "Sir Fig Newton and the Science of Persistence" by Sonja Thomas
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.
