cannon

Cannon and canon are occasionally confused by writers, but the two words have independent origins, and do not share a meaning. Cannon is most frequently found used in the sense of "a large gun," and can be traced to the Old Italian word cannone, which means "large tube." Canon, however, comes from the Greek word kanōn, meaning "rule." Although canon has a variety of meanings, it is most often found in the senses of "a rule or law of a church," "an accepted rule," or "a sanctioned or accepted group or body of related works." A loose cannon is "a dangerously uncontrollable person or thing." There are no loose canons.