keystone
noun /ˈkiːstəʊn/
/ˈkiːstəʊn/
- (architecture) the central stone at the top of an arch that keeps all the other stones in positionTopics Buildingsc2
- [usually singular] the most important part of a plan or argument that the other parts depend on
- Changes to the welfare system are the keystone of the government’s reforms.