piston /ˈpɪstən/noun 2verb 1forms 3 noun2 •A solid disk or cylinder that fits inside a hollow cylinder, and moves under pressure (as in an engine) or displaces fluid (as in a pump) •A valve device in some brass instruments for changing the pitch verb1 •To move up and down or in and out like a piston. formspistoned · pistoning · pistons
