(plural only) The formal robes of a priest.

(Internet) A URL presented in canonical form.

Present in a canon, religious or otherwise.

According to recognised or orthodox rules.

Stated or used in the most basic and straightforwardly applicable manner.

Prototypical.

(religion) In conformity with canon law.

(music) In the form of a canon.

(religion) Of or pertaining to an ecclesiastical chapter

(mathematics, computing) In canonical form.

(mathematics) Distinguished among entities of its kind, so that it can be picked out in a way that does not depend on any arbitrary choices.

(fandom slang) Part of canon (“the main continuity of a fictional universe”).