: not known or not well-known
also
: having an unknown value
an unknown quantity
1
: one that is not known or not well-known
especially
: a person who is little known (as to the public)
2
: something that requires discovery, identification, or clarification: such as
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
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, 30 Oct. 2025
Other causes can include infection and genetic conditions, though in some cases, the exact cause of Sudden Death Syndrome can be unknown.
—Taijuan Moorman, USA Today, 30 Oct. 2025
Soo Kim, MSNBC Newsweek, 27 Oct. 2025
And there’s still a lot of unknowns.
—Molly Castle Work, Twin Cities, 21 Oct. 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, 30 Oct. 2025
Other causes can include infection and genetic conditions, though in some cases, the exact cause of Sudden Death Syndrome can be unknown.
—Taijuan Moorman, USA Today, 30 Oct. 2025
Noun
There's too many unknowns here for just a spot treatment.
—Soo Kim, MSNBC Newsweek, 27 Oct. 2025
And there’s still a lot of unknowns.
—Molly Castle Work, Twin Cities, 21 Oct. 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 31 Oct. 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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