[DirectorTsaarx]

From the Merriam-Webster Online dictionary:
The "two-n" Cannon:

Main Entry: cannon
Function: noun
Inflected Form(s): plural cannons or cannon
Etymology: Middle French canon, from Italian cannone, literally, large tube, augmentative of canna reed, tube, from Latin, cane, reed -- more at CANE
Date: 15th century
1 plural usually cannon a : a large heavy gun usually mounted on a carriage b : a heavy-caliber automatic aircraft gun firing explosive shells
2 or can·on : the projecting part of a bell by which it is hung
3 : the part of the leg in which the cannon bone is found

And the "one-n" Canon:

Main Entry: can·on
Function: noun
Etymology: Middle English, from Old English, from Late Latin, from Latin, ruler, rule, model, standard, from Greek kanOn
Date: before 12th century
1 a : a regulation or dogma decreed by a church council b : a provision of canon law
2 [Middle English, prob. from Old French, from Late Latin, from Latin, model] : the most solemn and unvarying part of the Mass including the consecration of the bread and wine
3 [Middle English, from Late Latin, from Latin, standard] a : an authoritative list of books accepted as Holy Scripture b : the authentic works of a writer c : a sanctioned or accepted group or body of related works <the canon of great literature>
4 a : an accepted principle or rule b : a criterion or standard of judgment c : a body of principles, rules, standards, or norms
5 [Late Greek kanOn, from Greek, model] : a contrapuntal musical composition in two or more voice parts in which the melody is imitated exactly and completely by the successive voices though not always at the same pitch