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

In ecosystems, keystone species—like beavers or sea stars—are small but essential. —Scott Hutcheson, Forbes.com, 31 Mar. 2025

Faith Hillard, a senior zoological specialist at SeaWorld San Diego, said education is central to this experience because jellyfish can be a keystone species that helps indicate the general health of the ocean. —Natallie Rocha, San Diego Union-Tribune, 17 Mar. 2025

Jaguars are keystone species in the Amazon Rainforest and hold significant cultural meaning for many Indigenous people. —Photovogue, Vogue, 4 Mar. 2025

In natural environments, keystone species—such as wolves in Yellowstone or coral in marine ecosystems—do not attempt to control the entire system. —Scott Hutcheson, Forbes, 19 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