ETYM French piston; cf. Italian pistone piston, also pestone a large pestle; all from Latin pinsere, pistum, to pound, to stamp. Related to Pestle, Pistil.
A part of a machine that has a plunging or thrusting motion; SYN. plunger.
Barrel-shaped device used in reciprocating engines (steam, gasoline, diesel oil) to harness power. Pistons are driven up and down in cylinders by expanding steam or hot gases. They pass on their motion via a connecting rod and crank to a crankshaft, which turns the driving wheels. In a pump or compressor, the role of the piston is reversed, being used to move gases and liquids. See also internal-combustion engine.

(Hamor) (1894-1976) US composer and teacher. He wrote a number of textbooks, including Harmony 1941 and Orchestration 1955. His Neo-Classical works include eight symphonies, a number of concertos, chamber music, the orchestral suite Three New England Sketches 1959, and the ballet The Incredible Flutist 1938.
He was well regarded as a teacher; his pupils included Leonard Bernstein. He taught at Harvard University 1944–60.

In music, on a brass instrument, a valve which alters the length of tubing through which air vibrates, changing the pitch. The first valve lowers the pitch a whole tone, the second a semitone, the third three semitones. Most orchestral brass instruments today employ three valves, but sometimes a fourth is added.