batement light

[beyt-muh nt]
noun
  1. a compartment of a window with tracery, the bottom of which is formed by the arched head of a compartment or compartments below.

Origin of batement light

1400–50; late Middle English; short for abatement
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018