keystone

[kee-stohn]

noun

1. the wedge-shaped piece at the summit of an arch, regarded as holding the other pieces in place.

2. something on which associated things depend.

   the keystone of one's philosophy.

   Synonyms: linchpin, foundation, principle, basis

3. Also called keystone sack. Baseball Slang.,  second base.

keystone

/ ˈkiːˌstəʊn /

noun

1. Also called: headstone.  quoin. the central stone at the top of an arch or the top stone of a dome or vault

2. something that is necessary to connect or support a number of other related things

Word History and Origins

Origin of keystone¹

First recorded in 1630–40; key ¹ + stone

Example Sentences

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.

Read more on The Wall Street Journal

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.

Read more on Barron's

Some scientists trying to recover sunflower sea stars see the finding as a strong guide for future research — and efforts to boost the decimated keystone species.

Read more on Los Angeles Times

Despite the pile-up of particulars, Metcalfe knows he must find the lost poem, that it is the keystone without which the story crumbles into insignificance.

Read more on Los Angeles Times

The orangutan is a keystone species and plays a vital role in maintaining the health of the ecosystem.

Read more on Salon

Related Words

• base 
• cornerstone 
• foundation 
• fundament