noun (n)

• someone who maintains and audits business accounts(noun.person)

  Synonym:
  accountant, comptroller
  

  source: wordnet30
• a person who directs and restrains(noun.person)

  Synonym:
  restrainer
  

  source: wordnet30
• a mechanism that controls the operation of a machine(noun.artifact)

  Example:
  The speed controller on his turntable was not working properly.
  

  Synonym:
  control
  

  source: wordnet30
• One who, or that which, controls or restraines; one who has power or authority to regulate or control; one who governs.(noun)

  source: webster1913
• Any electric device for controlling a circuit or system;(noun)

  source: webster1913