Real Dictionary

piston
countable noun: A piston is a cylinder or metal disc that is part of an engine. Pistons slide up and down inside tubes and cause various parts of the engine to move.

Piston in American English
the snug-fitting engine part that is forced back and forth within a cylinder by the pressure of combustion, steam, etc. and a reciprocating connecting rod
Walter1894-1976; U.S. composer
noun: a disk or cylindrical part tightly fitting and moving within a cylinder, either to compress or move a fluid collected in the cylinder, as air or water, or to transform energy imparted by a fluid entering or expanding inside the cylinder, as compressed air

piston in Automotive Engineering
noun: A piston is a cylinder that is part of an engine. Pistons slide up and down inside tubes and cause various parts of the engine to move.

piston in British English
noun: a disc or cylindrical part that slides to and fro in a hollow cylinder. In an internal-combustion engine it is forced to move by the expanding gases in the cylinder head and is attached by a pivoted connecting rod to a crankshaft or flywheel, thus convert