c. 1300, ordinaunce, "an authoritative direction, decree, or command" (narrower or more transitory than a law), from Old French ordenance (Modern French ordonnance) or directly from Medieval Latin ordinantia, from Latin ordinantem (nominative ordinans), present participle of ordinare "put in order," from ordo (genitive ordinis) "row, rank, series, arrangement" (see order (n.)). By early 14c. senses had emerged of "arrangement in ranks or rows" (especially in order of battle), also "warlike provisions, equipment" (a sense now in ordnance).
"cannon and great guns collectively, artillery," 1540s, an old, clipped form of ordinance (q.v.) which word was attested from late 14c. in the sense of "military materials, provisions of war;" a sense now obsolete but which led to the specialized meanings "engines for discharging missiles" (early 15c.) and "branch of the military concerned with stores and materials" (late 15c.). The shorter word was established in these distinct senses by 17c.
The Ordnance survey (1833), an official geographical survey of Great Britain and Ireland, was undertaken by the government under the direction of the Master-General of the Ordnance (the natural choice, gunners being thoroughly trained in surveying ranges and distances).
It forms all or part of: adorn; alarm; aristarchy; aristo-; aristocracy; arm (n.1) "upper limb of the body;" arm (n.2) "weapon;" armada; armadillo; armament; armature; armilla; armistice; armoire; armor; armory; army; art (n.) "skill as a result of learning or practice;" arthralgia; arthritis; arthro-; arthropod; arthroscopy; article; articulate; artifact; artifice; artisan; artist; coordination; disarm; gendarme; harmony; inert; inertia; inordinate; ordain; order; ordinal; ordinance; ordinary; ordinate; ordnance; ornament; ornate; primordial; subordinate; suborn.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit irmah "arm," rtih "manner, mode;" Armenian arnam "make," armukn "elbow;" Greek arti "just," artios "complete, suitable," artizein "to prepare," arthron "a joint;" Latin ars (stem art-) "art, skill, craft," armus "shoulder," artus "joint," arma "weapons;" Old Prussian irmo "arm;" German art "manner, mode."
early 15c., "confirmation or enactment of a law," from Latin sanctionem (nominative sanctio) "act of decreeing or ordaining," also "decree, ordinance," noun of action from past-participle stem of sancire "to decree, confirm, ratify, make sacred" (see saint (n.)). Originally especially of ecclesiastical decrees.
"special ordinance or regulation promulgated by authority," early 14c., originally ecclesiastical, secular use is by late 14c., from Old French decre, variant of decret (12c., Modern French décret), from Latin decretum, neuter of decretus, past participle of decernere "to decree, decide, pronounce a decision," from de (see de-) + cernere "to separate" (from PIE root *krei- "to sieve," thus "discriminate, distinguish").