"steward," Middle English reve, refe, reive, rive, from Old English gerefa "king's officer," an Anglo-Saxon official of high rank, having local jurisdiction under a king, usually charged with administration of the affairs of a town or district. A word of unknown origin and with no known cognates, it is not considered to be connected to German Graf (see margrave). Compare sheriff. In Middle English also of manorial managers (c. 1300), an agent or steward of God (late 14c.). The mid-15c. "Life of St. Norbert" calls the Devil a wikkid reue. Related: Reeveship.
1640s (in Anglo-Latin from early 14c.), shortening of posse comitatus "the force of the county" (1620s, in Anglo-Latin from late 13c.), from Medieval Latin posse "body of men; power," from Latin posse "have power, be able" (see potent) + comitatus "of the county," genitive of Late Latin word for "court palace" (see comitatus). General sense of "an armed force" is from 1640s; the modern slang meaning "small gang" probably is from Western movies.
Posse comitatus, the power of the county; in law, the body of men which the sheriff is empowered to call into service to aid and support him in the execution of the law, as in case of rescue, riot, forcible entry and occupation, etc. It includes all male persons above the age of fifteen. In Great Britain peers and clergymen are excluded by statute. The word comitatus is often omitted, and posse alone is used in the same sense. [Century Dictionary]
"an emperor, a ruler, a dictator," late 14c., cesar, from Cæsar, originally a surname of the Julian gens in Rome, elevated to a title after Caius Julius Caesar (100 B.C.E.-44 B.C.E.) became dictator; it was used as a title of emperors down to Hadrian (138 C.E.). The name is of uncertain origin; Pliny derives it from caesaries "head of hair," because the future dictator was born with a full one; Century Dictionary suggests Latin caesius "bluish-gray" (of the eyes), also used as a proper name. Also compare caesarian.
Old English had casere, which would have yielded modern *coser, but it was replaced in Middle English by keiser (c. 1200), from Norse or Low German, and later by the French or Latin form of the name. Cæsar also is the root of German Kaiser and Russian tsar (see czar). He competes as progenitor of words for "king" with Charlemagne (Latin Carolus), as in Lithuanian karalius, Polish krol.
The use in reference to "temporal power as the object of obedience" (contrasted with God) is from Matthew xxii.21. Caesar's wife (1570s) as the figure of a person who should be above suspicion is from Plutarch. In U.S. slang c. 1900, a sheriff was Great Seizer.