in the ancient church, were a sort of testimonials of the orthodox faith, which the bishops and clergy sent each other to keep up the Catholic communion, and distinguish orthodox Christians from Arians and other heretics. They were denominated canonical, either as being composed according to a certain rule or form, or because they were given to the canonici, that is, those comprehended in the canon or catalogue of their church. When they had occasion to travel into other dioceses or countries, dismission and recommendatory letters, also letters of peace, &c. were so many species of canonical letters.

CANONICAL is also an appellation given to those epistles in the New Testament, more frequently called catholic or general epistles.