pendentive

This term is a specialized architectural descriptor used almost exclusively in the context of Byzantine and Renaissance architecture. It describes a specific structural solution to the geometric problem of placing a circular dome over a square room, creating a seamless transition that allows the weight of the dome to be concentrated on four piers.

Because it is a technical term of art, it is rarely encountered outside of architectural history, engineering, or art history texts. It should not be confused with a squinch, which is a different method of achieving the same transition using a diagonal arch across the corners of the square base.