Definition of keystone:
groundwork, footing, warp, brace, scaffold, ground tackle, basis, key fruit, back, tombstone, underpinning, burning issue/question, anchorperson, anchor, rachis, pillar, key, gantry, framework, moxie, prop, samara, root, backbone, frame, spinal column, paint, priority, tonality, anchorman, gravestone, joist, cornerstone, vertebral column, concern, essence, element, core, spine, foundation, cay, warp and woof, support, linchpin, ground, buttress, gumption, mainstay, bedrock, bottom, feature, guts, headstone, sand, stanchion, rafter, grit, lynchpin, staple, winder.
- "America To-day, Observations and Reflections", William Archer.
- "Hills and the Sea", H. Belloc.
- "The Psychology of Beauty", Ethel D. Puffer.