In the 13c, 'kerns' signified those who attached themselves to the establishments of English lords in Ireland. They were considered idlers and spongers. Later the term was used of a fighting man from Ireland, a foot soldier without armour. When fighting at close quarters the kern used a battle-axe much like that used by the Vikings. The Latin form was kernus or homo de kerne. [< Ir. ceithearn = band of soldiers] -
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.