piston

A solid cylinder or disk that fits snugly into a larger cylinder and moves under fluid pressure, as in a reciprocating engine, or displaces or compresses fluids, as in pumps and compressors.

A valve mechanism in brass instruments for altering the pitch.

In machinery, a movable piece, generally of a cylindrical form, so fitted as to fill the sectional area of a tube, such as the barrel of a pump or the cylinder of a steam-engine, and capable of being driven alternately in two directions by pressure on one or the other of its sides.

In musical wind-instruments of the trumpet family, one of the forms of valve whereby a crook is temporarily added to the tube and the pitch of the tones altered.

In organ-building, a thumb-knob which may be pushed in like a piston, whereby some change in registration is pneumatically effected; a pneumatic coupler or combination knob.

The central retractile part of the acetabulum or sucker of a cephalopod, whose action in producing a vacuum resembles that of the piston of an air-pump.

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.

that part of a piston which is made fast to the piston rod.

a rod by which a piston is moved, or by which it communicates motion.

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.