Real Dictionary

mechanism
In a machine or piece of equipment, a mechanism is a part, often consisting of a set of smaller parts, which performs a particular function.
countable noun: A mechanism is a part of your behaviour that is automatic and that helps you to survive or to cope with a difficult situation.
countable noun: A mechanism is a special way of getting something done within a particular system.

mechanism in American English
the working parts or arrangement of parts of a machine; works
noun: an assembly of moving parts performing a complete functional motion, often being part of a large machine; linkage

mechanism in British English
noun: a system or structure of moving parts that performs some function, esp in a machine

mechanism in Mechanical Engineering
noun: A mechanism is a system or structure of moving parts that performs a particular function, especially in a machine.