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 of keystone

• 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

Housing is the keystone that impacts multiple issues most important to San Jose’s residents. —Mercury News Editorial Board, Mercury News, 26 May 2026

And for United Airlines CEO Scott Kirby, a keystone habit for leading the $30 billion airline is taking a 20-minute nap on the floor, which his staff initially found bizarre. —Julian Hayes Ii, Forbes.com, 22 May 2026

But the Cuyahoga River combusting due to pollutants from corporate dumping was one of the keystone events in the creation of the Environmental Protection Agency. —Chicago Tribune, 4 May 2026

An optical-first keystone design is only one part of the projector's full optical image optimization suite. —Paul Ridden may 01, New Atlas, 1 May 2026

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