mechanism
mech.a.nism \'mek-*-.niz-*m\ n 1a: a piece of machinery 1b: a process or technique for achieving a result 2: mechanical operation or action 3: a doctrine that holds natural processes (as of life) to be mechanically determined and capable of complete explanation by the laws of physics and chemistry 4: the fundamental physical or chemical processes involved in or responsibl e for an action, reaction, or other natural phenomenon