cornerstone
Concise Oxford English Dictionary © 2008 Oxford University Press:
cornerstone/ˈkɔːnəstəʊn/
▶noun
- 1 a stone that forms the base of a corner of a building, joining two walls.
- 2 an important quality or feature on which something is based: a minimum wage remained the cornerstone of policy.
'cornerstone' also found in these Oxford entries:

