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

Bison are a keystone species to North American prairies. —Fort Worth Star-Telegram, 29 Apr. 2026

Sea otters are a keystone species in kelp forest ecosystems, eating sea urchins that would otherwise consume the kelp, according to the aquarium. —Cierra Morgan, Los Angeles Times, 29 Apr. 2026

Setup is effortless thanks to Intelligent Screen Adaption, which features auto-focus, auto-keystone correction, and obstacle avoidance. —Juhi Wadia, PC Magazine, 23 Apr. 2026

Kim learned that beavers are a keystone species — an organism that holds an ecosystem together. —Elizabeth Hernandez, Denver Post, 16 Apr. 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