The Collaborative International Dictionary of English v.0.48:

Harquebus \Har"que*bus\ Harquebuse \Har"que*buse\
   (h[aum]r"kw[-e]*b[u^]s), n. [See Arquebus.]
   A firearm with match holder, trigger, and tumbler, made in
   the second half of the 15th century. The barrel was about
   forty inches long. A form of the harquebus was subsequently
   called arquebus with matchlock.
   [1913 Webster]