Origin of the word "gun"

From wordorigins.org:

Gun

This word for a firearm most likely comes from a Scandinavian woman's name. It was and is common practice to name siege engines and later cannon after women. Two famous examples are Mons Meg, the 15th century mortar that can be seen at Edinburgh castle, and Big Bertha of WWI fame. In this case, a weapon or weapons seem to have been named after a woman or women named Gunnhildr, and the name transferred over to the general sense.

Both gunnr and hildr mean war in Old Norse, making it an apt name for a weapon, even though there is no historical personage of significance named Gunhildr. There is at least one known example of a particular siege engine named Gunnhildr...variations on the general word gun appear in English records written in Latin starting in 1339. The first recorded use of of the word, gonne, in English is in 1384 by Chaucer.