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keystone

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keystone

Main Entry:: key·stone
Pronunciation:: \ˈkē-ˌstōn\
Function:: noun
Date:: circa 1637

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 : 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

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