A <em>cannon</em>, with two Ns, is a large mounted gun: "They fired the cannon at noon." A <em>canon</em>, with one N, is an accepted body of works or rules — "Austen is firmly in the literary canon", "that detail isn't canon". If it shoots, it takes the extra N.
The core difference
The two words are pronounced the same and differ by a single letter, which makes this one of the most common spelling slips in fan writing, journalism and academic prose alike. Their meanings are entirely unrelated.
How to use cannon
A cannon is heavy artillery — historically a smooth-bore gun on a carriage, now also the automatic gun mounted on an aircraft or armoured vehicle. It is a noun, and unusually its plural can be either cannons or cannon ("a battery of twelve cannon").
- "The fort still has three cannon pointing out to sea."
- "He's a loose cannon in meetings — nobody knows what he'll say."
- "Water cannon were deployed outside the stadium."
In British English it also works as a verb meaning to collide heavily: "He cannoned into the defender."
How to use canon
Canon has several established senses, all sharing the idea of an authorised list or standard:
- A body of works accepted as genuine or important: "the Shakespeare canon", "the Western literary canon".
- A rule or principle: "canon law", "the canons of good practice".
- In fandom, the official material of a fictional universe as opposed to fan invention: "Their relationship is canon."
- A member of clergy attached to a cathedral: "Canon Williams read the lesson."
- In music, a form where a melody is imitated in overlapping parts — a round is the simplest kind.
The memory trick
Count the Ns. Two Ns for the weapon, one N for the rule. If you need a hook: a cannon is the bigger, heavier thing, so it gets the extra letter. Alternatively, ask whether the word can be replaced by "official" or "accepted" — if yes, single N. If it can be replaced by "gun", double N.
The mistakes to watch for
The most frequent error goes one way: writers reach for cannon when they mean the accepted version of events, giving "that's not cannon" instead of "that's not canon". Watch too for the derived forms, which follow the same split — canonical, canonise and canonically all take one N, while cannonball and cannonade take two.
Finally, the camera brand is spelled Canon, with one N, which occasionally seeds confusion in product copy. It is a proper name and follows its own logic; do not treat it as evidence about either word.
Frequently Asked Questions
Is it "loose cannon" or "loose canon"?
"Loose cannon", two Ns. The image is an unsecured gun rolling around a ship's deck — an unpredictable danger. A loose canon would be a relaxed rule book.
In fandom, is it "canon" or "cannon"?
Canon, one N. It borrows the sense of an authorised body of texts, so anything established in the official material is canon, and everything else is fanon or headcanon.
What is the plural of cannon?
Both "cannons" and "cannon" are correct. The unchanged plural is common in military and historical writing — "forty cannon lined the ridge" — while "cannons" is fine in general use.