From a person to a place
In North American English, commissary usually names a store. Soldiers and their families shop at the grocery on a military post. Prisoners buy snacks and stamps from the canteen, or speak of money sitting on a commissary account. Film and television crews still eat in the studio commissary, a dining hall attached to the lot rather than a public restaurant. Those place-meanings are recent. For most of its English life the word named a person: someone a superior had charged with a defined duty.
Into Middle English
English took the noun in the late 1300s. Middle English wrote it commissarie, with spellings such as commyssary and comissarie. Dictionaries do not all tell the same borrowing story. Some treat Medieval Latin commissarius as the direct source. Others, including Merriam-Webster, put Anglo-French commissaire or commissarie in between. The Middle English Dictionary lists both Latin and Old French. The French and Latin forms are the same office-title, so English could have met the word in either language, or in both.
Dating is uneven as well. Historical surveys and the Middle English record place the word in the fourteenth century; a Wycliffite text from 1395 already uses commissariis for people said to act as God’s delegates in judging sin. Merriam-Webster’s first-known-use date of 1555 is later than that evidence and appears to mark a citation for one of its modern senses rather than the English debut. Concise Oxford-style notes agree on an ecclesiastical officer representing another in the 1300s, then an official in charge of supplies in the 1400s.
The origin of the word commissary is therefore not a shop at all. It is an official title: a person in charge because a charge had been committed to them.
What Latin put together
Medieval Latin commissarius is built in a transparent way. The stem is commiss-, from commissus, the past participle of committere, a verb that could mean to join, to send together, to place in someone’s keeping, or to entrust. English later borrowed that verb separately as commit. The ending is -arius, the usual Latin suffix for a person concerned with something, which English writes as -ary. A commissarius is, in outline, the person of the thing entrusted.
Committere itself is com- (with, together) plus mittere (to send, let go, put). The same Latin verb stands behind mission, message, and committee. French kept the official as commissaire, still used for police and other commissioners. Italian has commissario, Spanish comisario, German Kommissar. English later borrowed commissar through Russian and German, a doublet of commissary rather than a new root.
Church first, then the army
The earliest English uses sit in church and government. A bishop’s commissary exercised spiritual jurisdiction in distant parts of a diocese, or covered the see when the bishop was away. The word could also mean a papal legate, a royal delegate, or, at Oxford, the vice-chancellor acting as commissary general. In Scots law a commissary became the judge of a commissary court, which handled probate and related business; that legal sense is a later specialization, well established by the seventeenth century.
By the late fifteenth century the title had a military job: the officer responsible for food, stores, and transport. Britain later organized that work as a commissariat, with a commissary-general at its head and deputies beneath him. The person still came first. The department was named after the officials, not the other way around.
How the shop arrived
The leap from officer to building is American and comparatively late. In 1882 the United States military record shows commissary as a storeroom, especially a place that sold goods to people in a closed community of work. From the supply officer’s charge came the room where the supplies sat, then the store that sold them. In 1924 American English adds a dining room inside a larger workplace, the sense that Hollywood made familiar.
That chain is the usual account, but the links are not all equally sharp. The spread of the later meanings is not fully mapped. What is clear is the direction: office, then supply, then the place of supply, then a cafeteria that feeds the same captive workforce. The prison store and the inmate account are further American extensions of that closed-community shop.
In much of Europe the older official sense never gave way. French commissaire and German Kommissar still name commissioners and police ranks. English speakers who meet those titles are looking at cousins of the same Medieval Latin word, not at borrowings from the grocery on post.
A leftover deputy
The supermarket on a U.S. base still sells what a military commissary once had to issue. The title on the door is a leftover from the deputy who held the charge. If you want a single related form that keeps the person and drops the shop, commissar is the doublet that took a different European route and never became a cafeteria.