gearbox vs mechanism

gearbox

noun
  • That part of a car's transmission containing the train of gears, and to which the gear lever is connected. 

  • An enclosed gear train. 

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. 

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