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 removal of these keystone organisms devastated the grove’s structure, soil composition and hydrology, effectively collapsing the entire old-growth ecosystem.
—Scott Travers, Forbes.com, 24 May 2025
After losing longtime second baseman Gleyber Torres in free agency, the Yankees started the season with Jazz Chisholm Jr. at the keystone and a rotating cast of utility options filling in at third base.
—Peter Chawaga, MSNBC Newsweek, 21 May 2025
Acer has cooked in autofocus and auto keystone plus four-corner adjustment for setup ease.
—Paul Ridden
may 20, New Atlas, 20 May 2025
Other options include smart object avoidance and screen fit, plus manual keystone adjustment and digital zoom.
—PCMAG, 12 Mar. 2025
See All Example Sentences for keystone
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Scott Travers, Forbes.com, 24 May 2025
After losing longtime second baseman Gleyber Torres in free agency, the Yankees started the season with Jazz Chisholm Jr. at the keystone and a rotating cast of utility options filling in at third base.
—Peter Chawaga, MSNBC Newsweek, 21 May 2025
Acer has cooked in autofocus and auto keystone plus four-corner adjustment for setup ease.
—Paul Ridden
may 20, New Atlas, 20 May 2025
Other options include smart object avoidance and screen fit, plus manual keystone adjustment and digital zoom.
—PCMAG, 12 Mar. 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 6 Jun. 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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