combatant

belligerent

dogface, fighter, legionary, legionnaire, man-at-arms, regular, serviceman, soldier, trooper, warrior

servicewoman

carabineer (or carabinier), cavalier, cavalryman, cuirassier, dragoon

doughboy, footman, foot soldier, grunt, infantryman

commando, raider

jarhead [slang], marine, ranger

artilleryman, cannoneer, gunner, mortarman, musketeer, rifleman

archer, crossbowman

lancer, pikeman, spearman

Confederate, Continental, Federal, GI, guardsman, militiaman, minuteman

counterguerrilla (also counterguerilla), guerrilla (or guerilla), irregular, paramilitary, partisan (also partizan)

lifer, veteran, warhorse

conscript, draftee, enrollee, recruit

reservist

champion, knight

digger [chiefly Australian & New Zealand], gallowglass, gendarme