D defs.my
Entry 1 sense Webster, 1913

Piston

/pĭs'tən/ · Pis·ton · IPA /ˈpɪstən/
01 n. A sliding piece which either is moved by, or moves against, fluid pressure. It usually consists of a short cylinder fitting within a cylind…
  1. 1.
    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.(Mach.)
Phrases & compounds
Piston head — 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 — 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.