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

Shasta Lake, the state’s largest reservoir and the keystone of the federal Central Valley Project, stood at 94% of capacity on Friday, holding 116% of its historical average. —Sharon Bernstein, Sacbee.com, 11 Apr. 2025

Why is movement and spending time outside important? Movement and exercise have been described as keystone habits for weight loss. —Outside Online, 4 Mar. 2025

Repositioning the visuals is further helped by autofocus, auto keystone correction, fit-to screen and resizing to avoid obstacles. —New Atlas, 18 Apr. 2025

Mobilize Recovery is also partnering with keystone sponsors including Meta, iHeartMedia, Indivior, Braeburn, and SAMHSA’s Opioid Response Network, to enhance the reach and impact of the 2025 initiative. —Jem Aswad, Variety, 15 Apr. 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