mechanism vs piston

mechanism

noun
  • Any combination of cams, gears, links, belts, chains and logical mechanical elements. 

  • Any process of, or system designed to manage useful energy conversion. 

  • A mental, physical, or chemical process. 

  • The theory that all natural phenomena can be explained by physical causes. 

  • Any mechanical means for the conversion or control of motion, or the transmission or control of power. 

  • A group of entities, such as objects, that interact together. 

piston

noun
  • A valve device in some brass instruments for changing the pitch 

  • A solid disk or cylinder that fits inside a hollow cylinder, and moves under pressure (as in an engine) or displaces fluid (as in a pump) 

verb
  • To move up and down or in and out like a piston. 

How often have the words mechanism and piston occurred in a corpus of books? (source: Google Ngram Viewer )