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

• cornerstone
• basis
• foundation
• bedrock

Examples of keystone in a Sentence

Tourism is the city's economic keystone.

the keystone of his faith

Recent Examples on the Web

These keystone species are expected to play a crucial role in shaping the ecosystem. —Real-Time News Team, Miami Herald, 22 Aug. 2025

The Vali 1 is also designed to make setup a breeze courtesy of autofocus, auto keystone correction, screen alignment and image resizing to avoid obstacles. —New Atlas, 16 Aug. 2025

Kennedy has made children’s chronic disease a keystone of his position as the country’s top health official. —Berkeley Lovelace Jr, NBC news, 25 July 2025

The viewing rectangle can be scaled down and moved around to fit the available space, without needing to reposition the unit, and focus/keystone are automatically tweaked for easy placement. —New Atlas, 4 Aug. 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