‖n.; pl. Cornets-à-piston. [ F. ] (Mus.) A brass wind instrument, like the trumpet, furnished with valves moved by small pistons or sliding rods; a cornopean; a cornet. [ 1913 Webster ]

n. [ F. piston; cf. It. pistone piston, also pestone a large pestle; all fr. L. pinsere, pistum, to pound, to stamp. See Pestle, Pistil. ] (Mach.) A sliding piece which either is moved by, or moves against, fluid pressure. It usually consists of a short cylinder fitting within a cylindrical vessel along which it moves, back and forth. It is used in steam engines to receive motion from the steam, and in pumps to transmit motion to a fluid; also for other purposes. [ 1913 Webster ]

Piston head (Steam Eng.), that part of a piston which is made fast to the piston rod. --
Piston rod, a rod by which a piston is moved, or by which it communicates motion. --
Piston valve (Steam Eng.), a slide valve, consisting of a piston, or connected pistons, working in a cylindrical case which is provided with ports that are traversed by the valve. [ 1913 Webster ]

. (Mach.) A spring packing ring, or any of several such rings, for a piston. [ Webster 1913 Suppl. ]

. In a single-acting engine, an elongated hollow piston, open at the end, in which the end of the connecting rod is pivoted. The piston rod, crosshead and stuffing box are thus dispensed with. [ Webster 1913 Suppl. ]