mizzen (n.)

"aftermost fore-and-aft sail of a three-masted ship," early 15c., from Middle French misaine "foresail, foremast," altered (by influence of Italian mezzana "mizzen") from Old French migenne, from Catalan mitjana, from Latin medianus "of the middle" (from PIE root *medhyo- "middle"). The sense in this transmission must have been something other than "middle," or the thing described changed, because the "middle" mast on a ship is the mainmast. Klein suggests an alternate etymology of the French word from Arabic, via Italian.