pane

A pane is a piece of glass, especially one that fits into a window frame. If you hit your baseball through your neighbors' kitchen window, you'll probably owe them a new pane.

Panes are almost always made of glass, although occasionally they're some other translucent material. Stained-glass windows have colorful panes, and older houses with their original details often have windows made of many small glass panes. The original meaning of pane was "piece of a garment," from the Latin pannum, "piece of cloth." Later, a pane became "a panel of wood," and finally "a panel of glass."