linchpin
1. [ noun ] a central cohesive source of support and stability
Synonyms: anchor backbone lynchpin keystone mainstay
Examples:

"faith is his anchor" "the keystone of campaign reform was the ban on soft money" "he is the linchpin of this firm"

Related terms: support anchor
2. [ noun ] pin inserted through an axletree to hold a wheel on
Synonyms: lynchpin
Related terms: pin
Similar spelling:   lynchpin
  lion_cub