1
: the wedge-shaped piece at the crown of an arch that locks the other pieces in place see arch illustration
2
: something on which associated things depend for support
determination, a keystone of the puritan ethic—
L. S. Lewis
L. S. Lewis3
or keystone species
: a species of plant or animal that produces a major impact (as by predation) on its ecosystem and is considered essential to maintaining optimum ecosystem function or structure
Examples of keystone in a Sentence
Tourism is the city's economic keystone.
the keystone of his faith
Recent Examples on the Web
The administration's extraordinary action would remove a keystone of the country's climate regulation just as the world experiences unprecedented heat and climate-driven extreme weather disasters.
—Jeff Young, MSNBC Newsweek, 1 Sep. 2025
For many clients, something as simple as a daily walk becomes a keystone habit that influences sleep, stress levels, food choices, and energy throughout the day.
—Malana Vantyler, USA Today, 27 Aug. 2025
The New Yorker’s founding editor, Harold Ross, regarded The Talk of the Town as the keystone of each issue, and sent as much of it as possible through White’s typewriter.
—Nathan Heller, New Yorker, 24 Aug. 2025
These keystone species are expected to play a crucial role in shaping the ecosystem.
—Real-Time News Team, Miami Herald, 22 Aug. 2025
See All Example Sentences for keystone
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Jeff Young, MSNBC Newsweek, 1 Sep. 2025
For many clients, something as simple as a daily walk becomes a keystone habit that influences sleep, stress levels, food choices, and energy throughout the day.
—Malana Vantyler, USA Today, 27 Aug. 2025
The New Yorker’s founding editor, Harold Ross, regarded The Talk of the Town as the keystone of each issue, and sent as much of it as possible through White’s typewriter.
—Nathan Heller, New Yorker, 24 Aug. 2025
These keystone species are expected to play a crucial role in shaping the ecosystem.
—Real-Time News Team, Miami Herald, 22 Aug. 2025
See All Example Sentences for keystone
Cite this Entry
“Keystone.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/keystone. Accessed 9 Sep. 2025.
Copy CitationKids Definition
keystone
noun
key·stone
ˈkē-ˌstōn 
1
: the wedge-shaped piece at the top of an arch that locks the other pieces in place
2
: something on which other things depend
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