What is "sconcheon"

Squinch \Squinch\ (skw[i^]nch), n. [Corrupted fr. sconce.] (Arch.) A small arch thrown across the corner of a square room to support a superimposed mass, as where an octagonal spire or drum rests upon a square tower; -- called also sconce, and sconcheon.

n. (context architecture English) A squinch.