cornerstone: Meaning and Definition of

cor•ner•stone

1. a stone uniting two masonry walls at an intersection.
2. a stone representing the nominal starting place in the construction of a monumental building, usually carved with the date and laid with appropriate ceremonies.
3. something that is essential, indispensable, or basic: The cornerstone of democratic government is a free press.
4. the chief foundation on which something is constructed or developed: The cornerstone of his argument was that all people are created equal.