ˈpistən noun
( -s )
Etymology: French, from Middle French, large pestle, from Old Italian pistone, from pistare to beat, pound, trample down (from Medieval Latin pistare, from Latin pistus, past participle of pinsere to pound, crush) + -one, aug. suffix — more at pestle
1. : a sliding piece moved by or moving against fluid pressure and usually consisting of a short cylinder fitting within a cylindrical vessel along which it moves back and forth — compare cylinder 2b,2c, slide valve
2.
a. or piston valve : a sliding valve moving in a cylinder like an engine piston in a brass wind instrument and serving when depressed by a finger knob to add a crook to the tube and hence to lower its pitch
b. or piston knob : a push button on an organ console for bringing in a preselected registration