Milites

Milites were the trained regular footsoldiers of ancient Rome. These men were the non-specialist regular soldiers that made up the bulk of a Legion's numbers. Alongside soldiering, they also performed guard duties, labour work, building and other non-combat roles. Milites would usually have to serve for several years before becoming eligible for training to become immunes and thus become specialists with better pay.

The Latin term eventually became synonymous with "soldier", a general term that, in Western Europe, became associated with the mounted knight, because they composed the professional military corps during the Early Medieval Era. The same term, however, could mean the infantry soldier (Milites Pedites). Other usages include the "Milites Templi", referring to the Knights Templar, or Milites Sancti Jacobi (Order of Santiago).

From the Latin root "Miles" derived words such as "Military" and "Militia".

...
Wikipedia