piston

piston — noun

1. a solid metal part fitted inside a tube or cylinder, repeatedly sliding to press

1.nounC1
Definition

a solid metal part fitted inside a tube or cylinder, repeatedly sliding to press gas or liquid and drive the rest of a machine, especially an engine

Example

The mechanic replaced one cracked piston before the race on Sunday.

replace a piston

Inside the engine, each piston rose and fell in perfect time.

piston moving in an engine

Common collocations
  • engine piston
  • piston ring
  • piston rod
  • replace a piston
  • a seized piston
Synonyms
  • plunger

    broader term for a part that moves straight in and out, especially in pumps or hand tools

  • ram

    heavier industrial word, often used for hydraulic machinery that pushes with force

Grammar Patterns

engine piston

replace a piston

piston inside a cylinder

the piston slides back and forth

Usage Note

Usually named as part of an engine, pump, or brake system, often with words such as cylinder, ring, rod, replace, or seize. Distinguish from the cylinder: the piston is the part that moves inside it.

Common Mistakes

The cylinder was moving up and down.
The piston was moving up and down inside the cylinder.
the piston is the moving part; the cylinder is the space around it.

Synonym discussion

Sense: noun/1

These words all describe a part that moves in a straight line, but they are used in different machines. A 'piston' is the usual word for the sliding part inside an engine cylinder, and it is also used for similar parts in pumps or brake systems. A 'plunger' is broader and often suggests a part you push directly by hand or a simpler pump action. A 'ram' sounds heavier and more industrial, especially in hydraulic equipment that pushes hard against another object. A mechanic replaces a piston in a car engine, a coffee press has a plunger, and a factory machine may lift or lower a steel ram.

piston ↗plungerram ↗

Common collocations

Nouns

Phrases

  • replace a piston
  • a seized piston
  • piston ring
  • piston rod
  • piston inside a cylinder

Etymology

FrenchEnglish

English borrowed 'piston' from French during the period when machine design was developing quickly. The older French word referred to something that pounds or presses, which matches the way a piston drives and pushes inside a machine.