mech·a·nism 
(mĕkə-nĭz′əm)
(mĕkə-nĭz′əm)n.
1.
a. A machine or mechanical appliance.
b. The arrangement of connected parts in a machine.
2. A system of parts that operate or interact like those of a machine: the mechanism of the solar system.
3. An instrument or a process, physical or mental, by which something is done or comes into being: "The mechanism of oral learning is largely that of continuous repetition" (T.G.E. Powell).
4. A habitual manner of acting to achieve an end.
5. Psychology A usually unconscious mental and emotional pattern that shapes behavior in a given situation or environment: a defense mechanism.
6. The sequence of steps in a chemical reaction.
7. Philosophy The doctrine that all natural phenomena are explicable by material causes and mechanical principles.
[New Latin mēchanismus, from Late Latin mēchanisma, from Greek mēkhanē, machine; see MECHANIC.]