> The akritai (singular akrites) is a term used in the Byzantine Empire in the 9th–11th centuries to denote the frontier soldiers guarding the Empire's eastern border, facing the Muslim states of the Middle East. (Wikipedia)
Akron means edge or border, so "frontiersman" or "those of the border".
EDIT: Commenters seem upset about the Muslim part, I didn’t mean to imply anything, you cannot just copy-paste contemporary disputes and prejudices a thousand years ago. In the historical context it’s just like most borders between different civilizations. The point is that they were a collective organization getting together to defend their land.