keystone

noun

key·​stone ˈkē-ˌstōn 

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

3

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

Synonyms

• base
• basis
• bedrock
• bottom
• cornerstone
• footing
• foundation
• ground
• groundwork
• root
• underpinning
• warp
• warp and woof

Examples of keystone in a Sentence

Tourism is the city's economic keystone.

the keystone of his faith

Recent Examples on the Web

That has made Dover and Eaton , which have small portions of the data center as keystones of their stocks, considered washed up. —Jim Cramer, CNBC, 13 Apr. 2025

The keystone of our fiscal strategy is economic growth. —Wes Moore, Baltimore Sun, 12 Apr. 2025

As keystone species, parrotfish play a critical part in maintaining coral reef health by grazing on macroalgae that would otherwise suffocate coral—clearing space for reefs to regenerate. —Ashlee Marie Preston, Forbes.com, 27 Mar. 2025

The projector comes with auto (vertical) keystone correction and corner fit, plus screen alignment courtesy of Digital Image Shrink and vertical image positioning without having to move the unit via Digital Shift. —Paul Ridden, New Atlas, 15 Feb. 2025

Word History

First Known Use

circa 1637, in the meaning defined at sense 1

Rhymes for keystone

• alone
• atone
• backbone
• bemoan
• bluestone
• breastbone
• brownstone
• capstone
• cheekbone
• condone
• curbstone
• cyclone

Kids 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