The term "cornerstone" refers to a fundamental element or principle that holds or supports something together. It is often used metaphorically to indicate the most important part of a system, organization, or belief. In construction, a cornerstone is a stone placed at a corner of a building to indicate its start and support its structure.
The word "cornerstone" comes from Middle English "corner ston," which refers to a stone located at the corner of a building. The "corner" part has Germanic roots, while "stone" derives from the Old English "stan."