piston
/ˈpɪstən/noun
1- a disc or short cylinder fitting closely within a tube in which it moves up and down against a liquid or gas, used in an internal-combustion engine to derive motion, or in a pump to impart motion活塞。
1.1
- a valve in a brass musical instrument in the form of a piston, depressed to alter the pitch of a note（铜管乐器上的）活塞阀键。
词源
early 18th cent.: from French, from Italian pistone, variant of pestone 'large pestle', augmentative of pestello 'pestle'.