- the forestay that braces the mainmast

- 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"

- a prominent supporter
"he is a pillar of the community"

1. The stay extending from the foot of the foremast to the maintop.

2. Main support; principal dependence.

"The great mainstay of the Church." -- Buckle.