What is the meaning of arch in Greek?

The word "arch" doesn't have a direct single-word equivalent in ancient Greek that captures its architectural meaning. The concept was expressed descriptively. Words like ἀψίς (apsís), meaning "arch" or more generally "vault," are used to describe a curved structure, but it often refers to a semicircular or vaulted shape rather than just a simple arch. Other terms might be used depending on the context, describing the components or the overall structure.