keystone

Noun	1.	keystone - 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" backbone, linchpin, lynchpin, mainstay, anchor support - something providing immaterial support or assistance to a person or cause or interest; "the policy found little public support"; "his faith was all the support he needed"; "the team enjoyed the support of their fans"
	2.	keystone - the central building block at the top of an arch or vault headstone, key arch - (architecture) a masonry construction (usually curved) for spanning an opening and supporting the weight above it building block - a block of material used in construction work coign, coigne, quoin - the keystone of an arch

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