1. A law; a criterion or standard used in making judgments: The court proceedings had to comply to the canon of regulations.
2. A principle governing the affairs of people within or among political units.

The canons of good behavior apply to everyone.
3. A clergyman assigned to a large church, or who is a member of a special religious order: A canon is "someone who lives according to a religious rule" or canon.
4. Etymology: from Latin meaning "rule" or "law", which came from Greek kanon, "measuring rod, rule, standard".