A valve in an internal combustion engine mounted alongside the cylinder.
 Example sentencesExamples
-  Three more prototype cars were built, chassis number A3 was the third Aston Martin ever built and is the oldest in existence with a 1.5 litre 11 hp four cylinder side valve.
 -  Gasoline engines with overhead valves are less polluting than those with side valves.
 -  Twenty of these engines had side valves; the remainder were overhead valve engines.