- a light coming from the side
- a bit of incidental knowledge or information on a subject
- a window or opening in or at the side of a wall, door, etc.
- either of two running lights carried on the side of a ship or boat, a red one on the port side and a green one on the starboard
- A light coming from the side.
- Nautical Either of two lights, red to port, green to starboard, shown by ships at night.
- A piece of incidental or contrasting information.
- Usage Problem An additional activity; a sideline.
Usage Note: Sidelight is sometimes used to refer to an additional activity, no doubt by confusion with sideline. The Usage Panel does not cotton to this usage, with 77 percent rejecting it in our 2008 survey in He started his own trio in 1990. As a sidelight, he worked with Freddie Hubbard.