"officer whose duty is to receive and communicate the orders of a general officer," 1777, short for aide-de-camp (1660s), a French term in English, literally "camp assistant" (see aid (n.)). Plural of the full term is aides-de-camp.
c. 1200, "chief household officer;" c. 1300, "justice of the peace," from Old French conestable (12c., Modern French connétable), "steward, governor," principal officer of the Frankish king's household, from Medieval Latin conestabulus, from Late Latin comes stabuli, literally "count of the stable" (established by Theodosian Code, c. 438 C.E.), hence, "chief groom."
For first element, see count (n.1). Second element is from Latin stabulum "stable, standing place" (see stable (n.)). Probably the whole is a loan-translation of a Germanic word. Compare marshal (n.).
Meaning "an officer chosen to serve minor legal process" is from c. 1600, transferred to "police officer" by 1836. French reborrowed constable 19c. as "English police."
1810, "art of a general," from French stratégie (18c.) and directly from Greek strategia "office or command of a general," from strategos "general, commander of an army," also the title of various civil officials and magistrates, from stratos "multitude, army, expedition, encamped army," literally "that which is spread out" (from PIE root *stere- "to spread") + agos "leader," from agein "to lead" (from PIE root *ag- "to drive, draw out or forth, move"). In non-military use from 1887.
Italian police officer, 1660s, from Italian, "police officer, constable" (plural sbirri), from Late Latin birrus "red," from Greek pyrros "red," literally "fire-colored," from pyr "fire" (from PIE root *paewr- "fire"). With unetymological prefix (compare Spanish esbirro "henchman, minion," also Italian sbarra "barrier, cross-bar," etc.). Probably so called from the original color of the uniform.
title of a county or municipal officer with certain duties, mid-14c. (mid-13c. as a surname), corouner, from Anglo-French curuner, from Anglo-Latin custos placitorum coronae (late 12c.), originally the title of the officer with the duty of protecting the private property of the royal family, from Latin corona, literally "crown" (see crown (n.)).
In the Middle English period an elected county or borough officer charged with the supervision of pleas of the Crown and the administration of criminal justice. The duties of the office gradually narrowed and by 17c. the chief function was to determine the cause of death in cases not obviously natural.
late 14c., "one who takes the place of another," from Old French lieu tenant "substitute, deputy," literally "place holder" (14c.), from lieu "place" (see lieu) + tenant, present participle of tenir "to hold," from PIE root *ten- "to stretch." The notion is of a "substitute" for higher authority.
Specific military sense of "army officer next in rank to a captain and commanding the company in his absence" is from 1570s. Pronunciation with lef- is common in Britain, and spellings to reflect it date back to 14c., but the origin of this is a mystery (OED rejects suggestion that it comes from old confusion of -u- and -v-).