Fenestrella (fenestrella ©)

The translation in the title is followed by this sign ©; this means that it has been "invented" by me.

A window situated between the crypte (crypt) and the chœur (choir).
The window is located in the floor of the choir and lights the underlying crypt.
It is an Italian word for "small window".
Something similar can be found in the crypt of the church of Anzy-le-Duc; the window opening is located in the west wall of the crypt and opens onto the choir.

Anzy-le-Duc