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

City’s new keystone might not be as eye-catching on the pitch as Chelsea’s all-action attacker Rogers. — Cerys Jones, New York Times, 24 July 2026

After Jonathan India underwent shoulder surgery, the Royals handed the keystone reins to Michael Massey and Nick Loftin. — Kansas City Star, 23 July 2026

Bringing home a 1080p full HD smart projector equipped with ISA automatic focus and keystone correction for under $400 is an exceptional find. — Juhi Wadia, PC Magazine, 23 July 2026

The fest is a keystone event for Sandbox on the Beach, Santa Monica’s new civic plan for public events like the upcoming Super Bowl LXI and the LA28 Olympics and Paralympics. — Los Angeles Times, 16 July 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