1
a
: not known
It was a world and life, a way of being, utterly unknown to me.—
Avi
AviAn unknown number of cases go unreported.
For some unknown reason, the computer crashed.
b
: not well-known
an unknown writer/artist
When he left, he had been unknown. Now he was famous.—E. B. White
E. B. White2
: having an unknown value
an unknown quantity
1
a
: one that is not known or not well-known
especially
: a person who is little known (as to the public)
The director cast an unknown in the lead role.
b
the unknown
: a place, situation, or thing that is not known or understood
explorers venturing into the unknown
c
: something that is not known or not yet discovered
There are too many unknowns to go forward with the project.
2
a
: a symbol (such as x, y, or z) in a mathematical equation representing an unknown quantity
b
: a specimen (as of bacteria or mixed chemicals) required to be identified as an exercise in appropriate laboratory techniques
Synonyms of unknown
Examples of unknown in a Sentence
Adjective
a disease of unknown cause
Much remains unknown about his early life.
Her music was previously unknown outside of Asia.
An unknown number of cases go unreported.
The victim's attacker was unknown to her.
For some unknown reason, my computer crashed.
a book of unknown poems
Noun
explorers venturing off into the unknown
A fear of the unknown kept her from changing jobs.
The director cast an unknown in the lead role.
We're facing too many unknowns.
Recent Examples on the Web
Janay Reece, CBS News, 17 May 2026
The clock is ticking on Q-Day, the looming yet unknown date when quantum computing will have the capacity to quickly and easily break the encryption keys that keep most internet communication safe.
—Katie Hunt, CNN Money, 17 May 2026
Jill Lepore, New Yorker, 18 May 2026
Exact size unknown The asteroid originates from the asteroid belt, an area between Mars and Jupiter, Binzel explained.
—Jacopo Prisco, CNN Money, 18 May 2026
See All Example Sentences for unknown
Examples are automatically compiled from online sources to
show current usage.
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Opinions expressed in the examples do not represent those of Merriam-Webster or its editors.
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Adjective
Be cautious of unsolicited job offers, especially those received through text or direct message, and never respond to employment requests from unknown sources.
—Janay Reece, CBS News, 17 May 2026
The clock is ticking on Q-Day, the looming yet unknown date when quantum computing will have the capacity to quickly and easily break the encryption keys that keep most internet communication safe.
—Katie Hunt, CNN Money, 17 May 2026
Noun
Among the many unknowns of the Cold War was the extent to which the world was random or ordered.
—Jill Lepore, New Yorker, 18 May 2026
Exact size unknown The asteroid originates from the asteroid belt, an area between Mars and Jupiter, Binzel explained.
—Jacopo Prisco, CNN Money, 18 May 2026
See All Example Sentences for unknown
Cite this Entry
“Unknown.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/unknown. Accessed 20 May. 2026.
Copy CitationKids Definition
unknown
1 of 2 adjective
un·known
ˌən-ˈnōn 
: not known
also
: having an unknown value
an unknown quantity
unknown
2 of 2 noun1
: something that is unknown
2
: a symbol (as x, y, or z) representing a quantity whose value is unknown
an equation with two unknowns
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