mainstay mainstay /ˈmeɪnˌsteɪ/

noun

1. The forestay that braces the mainmast  ( mainstay )
   the forestay that braces the mainmast
   
2. A central cohesive source of support and stability  ( keystone , linchpin , lynchpin , anchor , backbone , mainstay )
   a central cohesive source of support and stability
    Faith is his anchor
   faith is his anchor
    The keystone of campaign reform was the ban on soft money
   the keystone of campaign reform was the ban on soft money
    He is the linchpin of this firm
   he is the linchpin of this firm
   
3. A prominent supporter  ( mainstay , pillar )
   a prominent supporter
    He is a pillar of the community
   he is a pillar of the community