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

What will climate change, and/or the ravages of resource extraction, do to this ecological and cultural keystone species? —Matthew Wills, JSTOR Daily, 10 Feb. 2025

Yet humans—the keystone species for fire on Earth—are merging the two arenas of earthly burning with a give and take that is reshaping the planet in what resembles a slow-motion Ragnarok. —Stephen Pyne, Smithsonian Magazine, 29 Jan. 2025

In a forest, keystone species—like wolves in Yellowstone—help balance the ecosystem by responding dynamically to changing conditions. —Scott Hutcheson, Forbes, 22 Jan. 2025

Yet humans – the keystone species for fire on Earth – are merging the two arenas of earthly burning with a give and take that is reshaping the planet in what resembles a slow-motion Ragnarok. —Stephen Pyne, The Conversation, 22 Jan. 2025

Word History

First Known Use

circa 1637, in the meaning defined at sense 1

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