I'm having a time out until I can learn some manners.
One instance being dialog and the other being a written item on a map seems like it could be even more precise use of both <a target="_blank" href="http://en.wikipedia.org/wiki/Cannon#Etymology_and_terminology">words</a>.
"Cannon" is derived from the Old Italian word cannone, meaning "large tube," which came from the Latin canna, in turn originating from the kanna,—Greek for "cane," or "reed"—and ultimately deriving from the Akkadian term qanu, meaning "tube" or "reed." The word "cannon" has been used to refer to a gun since 1326, in Italy, and 1418, in England. Bombardum, or bombard, was the earliest-used word for "cannon," but came to refer only to the largest weapons after 1430. "Cannon" serves both as the singular and plural of the noun, although the plural "cannons" is also correct.