: 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
PC Magazine, 30 Apr. 2025
The young man was decapitated after death for unknown reasons, although this was a ritualistic practice for some people during the Roman period.
—ArsTechnica, 30 Apr. 2025
Kevin Williams, Quartz, 17 Apr. 2025
Beyond the microbial unknowns, Batagaika’s deepening gash is a direct contributor to the climate crisis.
—Scott Travers, Forbes.com, 10 Apr. 2025
See All Example Sentences for unknown
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Adjective
Parents cannot read their kids' messages, but will receive alerts if the text messages contain images with explicit content, harmful words from unknown contacts, or links from unknown contacts.
—PC Magazine, 30 Apr. 2025
The young man was decapitated after death for unknown reasons, although this was a ritualistic practice for some people during the Roman period.
—ArsTechnica, 30 Apr. 2025
Noun
There are a lot of unknowns, and the administration communicates new changes daily.
—Kevin Williams, Quartz, 17 Apr. 2025
Beyond the microbial unknowns, Batagaika’s deepening gash is a direct contributor to the climate crisis.
—Scott Travers, Forbes.com, 10 Apr. 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 3 May. 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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