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

• 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

Its 3000 lumens brightness keeps content crystal clear even in daylight, and auto keystone alignment fixes the picture for you. —PC Magazine, 24 Oct. 2025

The habitat-modifying keystone species play a vital role in the region’s ecosystem supporting the health and dispersal of wildlife and other native plants. —John Leos, AZCentral.com, 23 Oct. 2025

Here, Landau functions more as an emotional keystone. —David Sims, The Atlantic, 23 Oct. 2025

Before we get started on the topic of human therapists that dip into AI to discover how generative AI and large language models provide therapy, let’s set the stage with a few keystones. —Lance Eliot, Forbes.com, 19 Sep. 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