: 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
Lauren Penington, Denver Post, 16 Oct. 2025
Whether the tunnel truly leads to Cleopatra’s resting place remains unknown, but the excavation offers a rare opportunity to revisit one of history’s most enduring mysteries, and possibly bring Egypt’s last queen closer to the surface once more.
—Kaif Shaikh, Interesting Engineering, 16 Oct. 2025
The Editorial Board, Oc Register, 13 Oct. 2025
The great unknown, of course, is the nature of the split.
—Andy Behrens, New York Times, 10 Oct. 2025
See All Example Sentences for unknown
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Adjective
Temperatures are dropping in Denver, but the date residents can expect the first hard freeze to hit the city remains unknown, according to National Weather Service meteorologists.
—Lauren Penington, Denver Post, 16 Oct. 2025
Whether the tunnel truly leads to Cleopatra’s resting place remains unknown, but the excavation offers a rare opportunity to revisit one of history’s most enduring mysteries, and possibly bring Egypt’s last queen closer to the surface once more.
—Kaif Shaikh, Interesting Engineering, 16 Oct. 2025
Noun
Imagine going out into the vast unknown, with limited provisions on small ships.
—The Editorial Board, Oc Register, 13 Oct. 2025
The great unknown, of course, is the nature of the split.
—Andy Behrens, New York Times, 10 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 17 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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