The Collaborative International Dictionary
Batement light
Batement \Bate"ment\, n. [For Abatement. See 2d Bate.]
Abatement; diminution.
--Moxon.
Batement light (Arch.), a window or one division of a window having vertical sides, but with the sill not horizontal, as where it follows the rake of a staircase.
Wiktionary
batement light
n. (context architecture English) A window or one division of a window having vertical sides, but with the sill not horizontal, as where it follows the rake of a staircase.