the.com/pane
A flat sheet of glass doing the hard work of keeping weather outside.
means A single sheet of glass set into a window, door, or frame.
from From Latin pannus, a piece of cloth, via French pan — once any flat panel or section, glass came later.
Cloth rootsOriginally meant a piece of fabric, not glass.
Window mathMultiple panes in one frame are panes, plural.
Homophone trapSounds like pain, unrelated despite window-cleaning suffering.