A central cohesive source of stability and security; a person or thing that is critical to a system or organisation.
A pin inserted through holes at the end of an axle or shaft, so as to secure a wheel or shaft-mounted device.
To adopt as, or serve as, a central cohesive source of stability and security.
The most important reason for, or element of, something.
The principal spring of a clockwork mechanism, which drives it by uncoiling.