c. 1300 as the name of the bright reddish-orange planet in the heavens; late 14c. as the name of the Roman god of war, from Latin Mars (stem *Mawort-), the Roman god of war (identified with Greek Ares), a name of unknown origin, apparently from earlier Mavors, related to Oscan Mamers.
According to Watkins the Latin word is from *Mawort- "name of an Italic deity who became the god of war at Rome ...." He also had agricultural attributes, and might ultimately have been a Spring-Dionysus. The planet was so named by the Romans, no doubt for its blood-like color. The Greeks also called the planet Pyroeis "the fiery." Also in medieval alchemy, "iron" (late 14c.). The Mars candy bar was first manufactured in 1932 by Forrest Mars Sr. of the candy-making family.
masc. proper name, from Latin Martinus, derivative of Mars (genitive Martis), Roman god of war (see Mars). In Elizabethan times, the parish of St. Martin-le-Grand in London was "celebrated as the resort of dealers in imitation jewellery" [OED].
late 14c., marcien "of, pertaining to, or characteristic of the planet Mars" (originally in reference to astrological influence), from Latin Martius "sacred to (the god) Mars; pertaining to (the planet) Mars," from Mars (genitive Martis; see Mars). From mid-15c. as "of or pertaining to the god Mars, warlike;" also sometimes "of or pertaining to the month of March" (1620s). The noun meaning "an inhabitant of the planet Mars" is attested by 1877.
late 14c., "warlike, of or pertaining to war," from Medieval Latin martialis "of Mars or war," from Latin Mars (genitive Martis), Roman god of war (see Mars). The sense of "connected with military organizations" (opposed to civil) is from late 15c. and survives in court-martial. Also, occasionally (with a capital M-), "pertaining to or resembling the planet Mars" (1620s). Related: Martially. Martial law, "military rule over civilians," first recorded 1530s. Martial arts (1909) as a collective name for the fighting sports of Japan and the surrounding region translates Japanese bujutsu.
third month of our year, first month of the ancient Roman calendar, c. 1200, from Anglo-French marche, Old French marz, from Latin Martius (mensis) "(month) of Mars," from Mars (genitive Martis). The Latin word also is the source of Spanish marzo, Portuguese março, Italian marzo, German März, Dutch Maart, Danish Marts, etc.
Replaced Old English hreðmonaþ, the first part of which is of uncertain meaning, perhaps from hræd "quick, nimble, ready, active, alert, prompt." Another name for it was Lide, Lyde (c.1300), from Old English hlyda, which is perhaps literally "noisy" and related to hlud "loud" (see loud). This fell from general use 14c. but survived into 19c. in dialect.
For March hare, proverbial type of madness, see mad (adj.). The proverb about coming in like a lion and going out like a lamb is since 1630s. March weather has been figurative of changeableness since mid-15c.