Mechanism

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.Biology. The involuntary and consistent response of an organism to a 
      given stimulus. 
      6.Psychology. A usually unconscious mental and emotional pattern that 
      shapes behavior in a given situation or environment: a defense mechanism. 
      7.The sequence of steps in a chemical reaction. 
      8.Philosophy. The doctrine that all natural phenomena are explicable by 
      material causes and mechanical principles. 
         
(dictionary.com)