What does keystone mean?
Keystone names two closely related ideas. In building, it is the wedge-shaped stone placed at the crown of an arch; by locking the arch's stones together, it stabilizes the whole structure. In ordinary usage, however, the word usually refers metaphorically to a person, institution, practice, or component whose importance is greater than its size or formal status might suggest. A keystone can therefore be the individual who connects a team, the principle that holds a philosophy together, or the policy on which a larger program depends. The term also has a specialized ecological use in phrases such as "keystone species," meaning a species with a disproportionately large effect on its ecosystem. Because it combines a literal architectural role with a broad figurative one, "keystone" is especially useful for describing a support that is indispensable but may not be conspicuous. It usually carries a positive, approving sense, suggesting that removing the person or element would seriously weaken or disrupt the whole.
nounA wedge-shaped stone at the crown of an arch that locks the other stones together and supports the structure. Figuratively, a person, thing, principle, or institution whose importance is essential to the stability or success of a larger whole.
- An indispensable person, thing, principle, or element that supports or connects a larger organization or system.
- The wedge-shaped stone placed at the crown of an arch, locking the arch's stones together and helping the structure remain stable.
- An organism or taxon whose ecological role has a disproportionately large effect on its community, as in "keystone species."
"Her ability to unite the committee made her the keystone of the project."
"Trust between the two departments was the keystone of the entire agreement."
"The masons carved an elaborate keystone for the central arch."
The regular plural refers to individual central arch stones or, figuratively, to multiple indispensable people, elements, or principles.
"The keystones of several arches were carved from pale limestone."
Remove the keystone from an arch—or the linchpin from a team—and the whole structure can come crashing down.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does keystone come from?
Keystone is a compound of "key" and "stone" that dates to Middle English. Its architectural sense refers to a locking stone at the crown of an arch, while the figurative sense developed by extension to something that secures or supports a larger whole. It is related in origin to "key" and English derivatives such as "keyword," "keynote," and "keyhole."
Related word forms
How keystone is actually used
The figurative use is the most common in modern English and generally carries an approving connotation. The architectural use is technical, while the ecological sense is usually expressed through established compounds such as "keystone species."
Easily confused with keystone
A keystone locks the stones of an arch together at its crown, whereas a cornerstone is a foundational block on which a structure rests.