What is the meaning of mechanism?

noun

• The atomic process that occurs during a chemical reaction.
  • usage: "he determined unique mechanisms for the photochemical reactions"
  • synonyms: chemical mechanism
• The technical aspects of doing something.
  • usage: "a mechanism of social control"; "mechanisms of communication"; "the mechanics of prose style"
  • synonyms: mechanics
• A natural object resembling a machine in structure or function.
  • usage: "the mechanism of the ear"; "the mechanism of infection"
• Philosophy) the philosophical theory that all phenomena can be explained in terms of physical or biological causes. (
• Device consisting of a piece of machinery; has moving parts that perform some function. .