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
Ca Wildfire Bot, Sacbee.com, 19 Dec. 2025
New South Wales state Police Commissioner Mal Lanyon said the men could be released soon after assessing that the specific threat posed by them was unknown, and officials would continue to monitor them.
—Reuters, NBC news, 19 Dec. 2025
Simone McCarthy, CNN Money, 17 Dec. 2025
But each of these evolving threats is a universe unto itself, with countless variables and unknowns.
—Kelso Harper, Scientific American, 16 Dec. 2025
See All Example Sentences for unknown
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Adjective
At this time, the containment status is unknown and the cause of the fire remains undetermined.
—Ca Wildfire Bot, Sacbee.com, 19 Dec. 2025
New South Wales state Police Commissioner Mal Lanyon said the men could be released soon after assessing that the specific threat posed by them was unknown, and officials would continue to monitor them.
—Reuters, NBC news, 19 Dec. 2025
Noun
For those living just over the de facto border, the vast unknowns about China’s project are already having an impact.
—Simone McCarthy, CNN Money, 17 Dec. 2025
But each of these evolving threats is a universe unto itself, with countless variables and unknowns.
—Kelso Harper, Scientific American, 16 Dec. 2025
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 Dec. 2025.
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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