- 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.