Definition of piston noun from the Oxford Advanced Learner's Dictionary



BrE BrE//ˈpɪstən//
; NAmE NAmE//ˈpɪstən//
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a part of an engine that consists of a short cylinder that fits inside a tube and moves up and down or backwards and forwards to make other parts of the engine move See related entries: Trains Word Originearly 18th cent.: from French, from Italian pistone, variant of pestone ‘large pestle’, augmentative of pestello ‘pestle’.
See the Oxford Advanced American Dictionary entry: piston