A warlike adjective
In current English, martial names what belongs to war, to soldiers, or to a soldierly manner. Martial music is written for the march. A martial bearing is the look of someone trained to fight. The same adjective sits inside two everyday compounds: martial law, when the army takes over civilian government, and court-martial, the military’s own tribunal. None of that vocabulary was coined on an English parade ground. The origin of the word martial is a Latin adjective that once meant, quite literally, of Mars.
Into Middle English from Latin
Writers in the later fourteenth century already used forms such as martial and martialle for things that were warlike or fit for fighting. Standard dictionaries place first English use in that century; some date the Middle English window more tightly to about 1325–1375. The source is Latin martialis, of or belonging to Mars. Accounts differ on the last hop. Several major dictionaries treat the loan as coming straight from Latin, including medieval Latin, where the adjective had already stretched from the god to war in general. Others allow Middle French martial as a possible intermediary. French itself had borrowed the same learned Latin form. Either path ends in one place: a Romance adjective built on the name of Rome’s war god.
Italian marziale, Spanish marcial, and Portuguese marcial keep the same Latin shape and the same military sense. They are the obvious living cousins.
Mars plus a suffix
Taken apart, the Latin word is transparent. The god’s name is Mars, genitive Martis, stem Mart-. The suffix -alis makes adjectives of belonging, the same ending English later inherited in legal, natal, and many other learned forms. Classical writers used martialis for what belonged to the cult of Mars. A flamen Martialis was the priest of that god. Cicero could call soldiers of the Legio Martia Martiales. The personal name Martialis, borne by the first-century epigrammatist known in English as Martial, is the same adjective used as a cognomen. Before English needed a word for warlike, Latin already had an everyday derivative of the god’s name.
How Mars got his own name is less settled, and it is honest to leave it unsettled. Old Latin also has Mavors. Oscan, a related Italic language, has Mamers. An archaic dedication on the Lapis Satricanus attests a form Mamartei. Reconstructions therefore swing between a Proto-Italic Mawortis and a form Mamart-, and the change from one to the other is not a regular sound law. A link to the Etruscan child-god Maris has been proposed and is not universally accepted. A further comparison with Sanskrit marut, the name of a band of storm deities, remains uncertain. What can be said with more confidence is that Mars in early Rome was not only a god of battle. He also had agricultural and seasonal associations, which is why the month Martius — English March — opened the old Roman year.
From the god to the army, then to the courtroom
The first English sense is the broad one: warlike, of war. By the late fifteenth century the adjective had a more institutional meaning, the military as opposed to the civil. That contrast is still audible in court-martial, a trial conducted by officers rather than by ordinary judges. Martial law, military rule imposed on civilians, is recorded from the 1530s. Both phrases keep the late-medieval coloring in which martialis had already come to mean military as much as mythological.
A capitalized Martial could, from the 1620s, mean pertaining to the planet Mars, named for the same god, almost certainly because of its reddish color. Older medical and alchemical writers also used martial of iron, the metal they paired with that planet. Those astronomical and chemical uses have largely fallen away. Martian took over for the planet, and iron compounds lost their martial labels. An obsolete noun martial once meant a soldier. What survived in ordinary prose is the military-and-warlike cluster.
Fighting systems, old phrase, new company
The pairing martial art is older than twentieth-century judo posters. Late medieval and Tudor English already spoke of an arte marcialle, or marcyall arte, as the craft of war, the knight’s skill at arms. In the early twentieth century the same English words were reused as a cover term for Japanese fighting methods, often as a rendering of bujutsu. From that point the plural martial arts came to name, for most speakers, East Asian combat sports and self-defense systems rather than European drill. The adjective did not change its Latin bones. Only the company it kept did.
Not the same word as marshal
English speakers who hear martial and marshal as identical have a genuine homophone pair and a genuine etymological trap. Marshal comes from Old French mareschal, ultimately a Germanic compound for a servant of horses, later a high officer of the court and the army. Martial never had a horse in it. It is Mars with an adjectival suffix, borrowed in the fourteenth century and still doing the god’s work whenever someone speaks of martial law, a martial air, or the martial arts. The month March and the given name Martin travel the same road from Mars. French mardi, Spanish martes, and Italian martedì still call Tuesday the day of Mars, while English replaced that god with Tiw, another war deity. The English adjective is the one that kept the Roman name in plain sight.