rifleman

Rifleman is built from rifle plus -man. Rifle traces back through Middle English riflen and Old French rifler to a Frankish word rīffilōn, itself from a Proto-Germanic verb formed with *rīfaną (to tear or scratch) and the suffix *-lōną — a nod to the grooves cut into a gun barrel. The -man part goes back through Old English mann to Proto-Germanic *mann-, simply meaning 'person.'

Rifle started as a verb about scoring or grooving something, then came to name the grooved firearm itself. Once rifle existed as a noun, English simply attached -man to it to name someone who carries and uses one.

Rifleman shares its second half with every other -man word in English, all descending from Old English mann — words like fisherman or postman follow the same pattern.