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.

Source: Webster's Revised Unabridged Dictionary (1913)