The Collaborative International Dictionary of English v.0.48:

Sconcheon \Scon"cheon\, n. (Arch.)
   A squinch.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]