keystone meaning and definition

KEYSTONE noun

Definition of keystone (noun)

1. a central cohesive source of support and stability
   • "faith is his anchor"; "the keystone of campaign reform was the ban on soft money"; "he is the linchpin of this firm"
   • synonyms: anchor, backbone, linchpin, lynchpin, mainstay
2. the central building block at the top of an arch or vault
   • synonyms: headstone, key