keystone
Americannoun
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the wedge-shaped piece at the summit of an arch, regarded as holding the other pieces in place.
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something on which associated things depend.
the keystone of one's philosophy.
- Synonyms:
- linchpin, foundation, principle, basis
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Also called keystone sack. Baseball Slang. second base.
noun
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Also called: headstone. quoin. the central stone at the top of an arch or the top stone of a dome or vault
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something that is necessary to connect or support a number of other related things
Etymology
Origin of keystone
Explanation
In a curved stone archway, the keystone is the one at the very center of the top. The keystone is the most important stone, and that's why this word is also used figuratively to mean the most important part of anything. A stone arch or vault gains its stability from the placement of the keystone, which is often the last one placed. From this architectural meaning, keystone also gained the figurative meaning of "central or most important part," or "the one thing upon which everything else depends." Like an actual stone keystone, this type lends stability: "The right to free speech is the keystone of all American rights."
Vocabulary lists containing keystone
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
She pointed to the 1967 Outer Space Treaty, a keystone document on international space law that President Lyndon Johnson signed onto.
From Salon • Apr. 9, 2026
Truth Social isn’t an especially strong keystone of this operation.
From Los Angeles Times • Mar. 3, 2026
Last year, some 1,000 U.S. troops withdrew from neighboring Niger, ending a nearly decadelong partnership that was the keystone of U.S. counterterrorism operations in the region.
From The Wall Street Journal • Nov. 2, 2025
They "play a central role in the food web, consuming fish and invertebrates and recycling nutrients" and are one of the "keystone species" of their ecosystem.
From Barron's • Oct. 10, 2025
The keystone of the state’s case was the six-page Plan of Action confiscated in the Rivonia raid.
From "Long Walk to Freedom" by Nelson Mandela
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
