Comitatus

The comitatus is the warband, the retinue of warriors led by their lord. Tacitus was the son-in-law of Agricola, one of the most famous early Roman emperors in Britain. Tacitus's work, _Agricola_ (ca. 43 A.D.) documents the military successes of his father-in-law, but the work is best known for its description of Germanic warband customs. Most of the information we have today on the warband code, its structure, and the relationship between the warlords and their kinsmen is taken from Tacitus's work.

According to Wikipedia, comitatus comes from the Latin, meaning company or armed group. Also it refers to a political term used in various meanings, in Europe's classical period and in the Middle Ages.