Etymology of Police
To police is the act of keeping order and controlling a region, district, sector, etc through the use of military (usually police) forces. A police force is an organized civil force that enforces the laws set by the government.
We start with the Ancient Greek politeuo (πολιτεύω) which means live as a citizen and the Greek word for city, polis. This word, politeuo, evolved into politeia (πολιτεία)—life of a citizen. In the beginning, police and policy meant the exact same thing, but this fact soon changed.
Later, when Latin arrived, the word politia (meaning government or state) came into existence and changed the meaning of the Ancient Greek word. The plural is politiae. Middle French eventually transformed the Latin politia into police, and English took that word and made it its own.
The book Policing and Contemporary Governance: The Anthropology of Police in Practice by W. Garriott has an interesting take on the relationship between police and governance. According to him, the etymology of police reveals that the two terms (governance and police) were once synonymous. He explains that the term police emerged in Western political discourse in the thirteenth century.
Police in Other Languages
Barnhart, Robert K., ed., Barnhart Dictionary of Etymology, H.W. Wilson Co., 1988.
de Vaan, Michiel. Etymological Dictionary of Latin and the other Italic Languages. Brill, 2008.
Murray, John. An Etymological Dictionary of Modern English. 1921.
William Campbell. Policing And Contemporary Governance. Print.