keystone

/ˈkiːstəʊn/ noun [C]

Definition

› the most important part of a plan, idea, etc. on which everything else depends: Selling overseas has been, and always will remain, one of the keystones of our national prosperity. A keystone of its corporate strategy is to invest in people, technology, and training to create a brand.

(Definition of keystone noun from the Cambridge Business English Dictionary © Cambridge University Press)