pis ‧ ton /ˈpɪst ə n/ BrE AmE noun [countable]
[ Date: 1700-1800 ; Language: French ; Origin: Italian pistone 'large stick for crushing' , from pistare 'to crush' ]
a part of an engine consisting of a short solid piece of metal inside a tube, which moves up and down to make the other parts of the engine move