What does cornerstone mean?
A cornerstone is, literally, one of the stones set at the corner of a building's foundation — historically the first stone laid, and often placed with a formal ceremony marking the start of construction. In modern English, however, the word is far more often used figuratively: a cornerstone is anything so essential that everything else depends on it, whether a principle ('freedom of the press is the cornerstone of democracy'), an institution, or even a person. The figurative use conveys strength, permanence, and indispensability, which makes the word a favourite of speeches, editorials, and formal writing. Its literal counterpart survives in architecture and civic tradition, where cornerstone-laying ceremonies remain a symbolic ritual for new public buildings. Related but distinct terms include 'keystone', which refers to the central stone of an arch rather than a corner. Whether describing masonry or ideas, cornerstone signals that something is foundational — remove it, and the whole structure is at risk.
nounA stone that forms the base of a corner in a building, traditionally laid at a ceremony to mark the start of construction; figuratively, something fundamental and indispensable that everything else depends upon.
- A stone positioned at the corner of a building's foundation, often laid with ceremony at the start of construction.
- (Figurative) A person, thing, or principle of fundamental importance on which everything else relies.
"Trust is the cornerstone of any lasting relationship."
"The mayor laid the cornerstone of the new library during a brief ceremony."
"Honest communication is the cornerstone of a healthy marriage."
Standard plural; used when referring to multiple literal stones or multiple foundational elements.
"The report identified three cornerstones of effective leadership."
The word 'cornerstone' has been laid into the foundations of the White House and countless public buildings — but its real power is metaphorical: it's the go-to term for whatever a system simply cannot stand without.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of cornerstone
Cornerstone is a straightforward English compound of 'corner' (from Old French 'corniere', ultimately from Latin 'cornu', meaning horn) and 'stone' (from Old English 'stān'). The compound arose in English, likely by the late medieval or early modern period, to describe the stone set at a building's corner. Its figurative extension — anything on which a larger structure depends — developed naturally from the architectural role of the first-laid, load-bearing stone, and is well established by the modern era.
How cornerstone is actually used
The figurative sense now dominates everyday usage, appearing frequently in formal writing, journalism, and speeches. It carries an unambiguously positive connotation of stability and importance. The ceremonial sense remains common in architecture and civic contexts.
Easily confused with cornerstone
A keystone is the wedge-shaped stone at the apex of an arch that locks the other stones in place, whereas a cornerstone sits at the corner of a building's foundation.