low-side window
/ˌləʊˌsʌɪd ˈwɪndəʊ/Church Archit.
noun
In some medieval churches: a small window lower than the other windows and typically situated in the chancel.
- The purpose of these windows is uncertain and has been the subject of much debate; they were popularly believed to provide a means by which lepers could view the altar..
Origin
Early 19th century; earliest use found in Thomas Rickman (1776–1841), architect. From low + side + window.