As has been said, both today and back in the day, some folks used the French few-ZEE or some approximation thereof and some (many?) Anglicized it in various ways. For reference the term in French originally referred to a fire-steel (and later the fire-making kit as well, according to one source that I've lost), then also the battery/hammer (frizzen) of a flint or pyrite snap-lock, and later the lock and/or the firearm itself. A websearch for fusil turns up a variety of other uses as well as the firearms one, with mostly Anglicized pronunciations, and various versions of:
n.
A light flintlock musket.
Etymologies
French, steel in a flintlock, firearm, from Old French fuisil, steel for a tinderbox, from Vulgar Latin *focīlis (petra), fire-(stone), from Late Latin focus, fire, from Latin, hearth.
Regards,
Joel
p.s., I think the modern French name for a fire steel may be briquet