keystoneEnglishOxford English Thesauruskeystone noun 1 a carved head formed the keystone of the door: cornerstone, central stone, quoin. 2 cooperation remains the keystone of the government's security policy: foundation, basis, linchpin, cornerstone, base, principle, guiding principle, core, heart, centre, crux, fundament, mainspring, priority.keystone Oxford Dictionary of English
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