How do you say cornerstone in Greek?

There isn't a single perfect translation for "cornerstone" in Greek that captures all its nuances. The best choice depends on the context. Here are a few options:

* Ακρογωνιαίος λίθος (akrogōniós líthos): This is a literal translation, meaning "corner stone." It's the most common and widely understood equivalent. It's suitable when referring to a literal cornerstone in a building.

* Βασικός λίθος (vasikós líthos): This translates to "basic stone" or "fundamental stone." It emphasizes the importance of the cornerstone as a foundational element, rather than its physical location.

* Θεμέλιος λίθος (themelios líthos): This means "foundation stone." It's a good choice when referring to something that is foundational or essential to a structure, idea, or system.

The best option will depend on whether you're talking about a literal cornerstone in architecture or a metaphorical cornerstone representing something fundamental. For most metaphorical uses, θεμέλιος λίθος (themelios líthos) or βασικός λίθος (vasikós líthos) might be preferable to the literal translation.