1. (

• anchor ,
• mainstay ,
• keystone ,
• backbone ,
• linchpin ,
• lynchpin

) 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" ;

2. (

• keystone ,
• key ,
• headstone

) the central building block at the top of an arch or vault ;