The Collaborative International Dictionary of English v.0.48:

canon \can"on\ (k[a^]n"[u^]n), n. [OE. canon, canoun, AS. canon
   rule (cf. F. canon, LL. canon, and, for sense 7, F. chanoine,
   LL. canonicus), fr. L. canon a measuring line, rule, model,
   fr. Gr. kanw`n rule, rod, fr. ka`nh, ka`nnh, reed. See
   Cane, and cf. Canonical.]
   1. A law or rule.
      [1913 Webster]

            Or that the Everlasting had not fixed
            His canon 'gainst self-slaughter.     --Shak.
      [1913 Webster]

   2. (Eccl.) A law, or rule of doctrine or discipline, enacted
      by a council and confirmed by the pope or the sovereign; a
      decision, regulation, code, or constitution made by
      ecclesiastical authority.
      [1913 Webster]

            Various canons which were made in councils held in
            the second centry.                    --Hook.
      [1913 Webster]

   3. The collection of books received as genuine Holy
      Scriptures, called the sacred canon, or general rule of
      moral and religious duty, given by inspiration; the Bible;
      also, any one of the canonical Scriptures. See Canonical
      books, under Canonical, a.
      [1913 Webster]

   4. In monasteries, a book containing the rules of a religious
      order.
      [1913 Webster]

   5. A catalogue of saints acknowledged and canonized in the
      Roman Catholic Church.
      [1913 Webster]

   6. A member of a cathedral chapter; a person who possesses a
      prebend in a cathedral or collegiate church.
      [1913 Webster]

   7. (Mus.) A musical composition in which the voices begin one
      after another, at regular intervals, successively taking
      up the same subject. It either winds up with a coda
      (tailpiece), or, as each voice finishes, commences anew,
      thus forming a perpetual fugue or round. It is the
      strictest form of imitation. See Imitation.
      [1913 Webster]

   8. (Print.) The largest size of type having a specific name;
      -- so called from having been used for printing the canons
      of the church.
      [1913 Webster]

   9. The part of a bell by which it is suspended; -- called
      also ear and shank.

   Note: [See Illust. of Bell.] --Knight.
         [1913 Webster]

   10. (Billiards) See Carom.
       [1913 Webster]

   Apostolical canons. See under Apostolical.

   Augustinian canons, Black canons. See under
      Augustinian.

   Canon capitular, Canon residentiary, a resident member of
      a cathedral chapter (during a part or the whole of the
      year).

   Canon law. See under Law.

   Canon of the Mass (R. C. Ch.), that part of the mass,
      following the Sanctus, which never changes.

   Honorary canon, a canon[6] who neither lived in a
      monastery, nor kept the canonical hours.

   Minor canon (Ch. of Eng.), one who has been admitted to a
      chapter, but has not yet received a prebend.

   Regular canon (R. C. Ch.), one who lived in a conventual
      community and followed the rule of St. Austin; a Black
      canon.

   Secular canon (R. C. Ch.), one who did not live in a
      monastery, but kept the hours.
      [1913 Webster]