- A central stone at the summit of an arch that locks all the stones into place and supports the weight of the structure above it.
- A central or crucial element or part that holds a structure or system together.
The word 'keystone' comes from the latin word 'capstone' which means 'central stone'.
- The keystone of the arch was carefully carved to fit into place and hold the weight of the structure above it.
- The keystone of the company's success was its commitment to customer satisfaction.
- The keystone species of the ecosystem play a crucial role in maintaining the balance of the environment.
- The keystone of the argument was the evidence that was presented in court.
- The keystone of the project was the cooperation and teamwork of all the members involved.