sidelight

side +‎ light

sidelight (plural sidelights)

1. A light found at the side of something; especially of a vehicle.

   If it starts getting misty, put your sidelights on.

2. A window found at one or both sides of a door.
3. A piece of incidental information that helps one understand a subject.
   • 1962 October, “New Reading on Railways: The Flying Scotsman 1862-1962. By C. Hamilton Ellis. Allen & Unwin. 6s.”, in Modern Railways, page unnumbered:

     He is well up to form when dealing with passenger stock, notably Victorian and Edwardian and on this and on East Coast motive power he throws many sidelights.

• “sidelight”, in Lexico, Dictionary.com; Oxford University Press, 2019–2022.