There are 2 main definitions of keystone in English:


Line breaks: key|stone
Pronunciation: /ˈkiːstəʊn


1A central stone at the summit of an arch, locking the whole together.
More example sentences
  • The final seven rusticated bands are precisely linked to the voussoirs and keystones that define the arches and the niches, the latter exactly the same height as the rectangular openings below.
  • The windows are surmounted by rusticated wooden jack arches with superimposed keystones, and a heavy modillion cornice crowns the bold Georgian proportions of the facade.
  • With a thickness of 12 inches, the arch features a decorative keystone and double corbels, outlined by antique glazing on a white lacquer base.
1.1The central principle or part of a policy, system, etc., on which all else depends: cooperation remains the keystone of the government’s security policy
More example sentences
  • Property rights, of course, form one of the keystones of the Anglosphere system.
  • This win-win strategy is the keystone of the economic policy framework of the Government.
  • People and the planet on which we live should be the primary referents of security in the 21st century, and human and global security should be the keystones of Australia's foreign and defence policies.
foundation, basis, linchpin, cornerstone, base, principle, guiding principle, core, heart, centre, crux, fundament, mainspring, priority

Definition of keystone in: