Marshal (also spelled marshall) is a term used in several official titles in various branches of society. As marshals became trusted members of the courts of Medieval Europe, the title grew in reputation. During the last few centuries, it has been used for elevated offices, such as in military rank and civilian law enforcement.
"Marshal" is an ancient loanword from Old (Norman) French (cf. modern French maréchal), which in turn is borrowed from Old Frankish *marhskalk (="stable boy, keeper, servant"), being still evident in Middle Dutch maerscalc, marscal, and in modern Dutch maarschalk (="military chief commander"; the meaning influenced by the French use).
It is cognate with Old High German mar(ah)-scalc "id.", modern German (Feld-)Marschall (="military chief commander"; again, the meaning influenced by the French use).
It originally and literally meant "horse servant", from Germanic *marha- "horse" (cf. English mare and modern German Mähre, meaning "horse of bad quality") and skalk- "servant" (cf. Old Engl. scealc "servant, soldier" and outdated German Schalk, meaning "high-ranking servant"). This "horse servant" origin is retained in the current French name for farrier: maréchal-ferrant.
The late Roman and Byzantine title of comes stabuli ("count of the stables") was adopted as a Latin analogue, which has become the French connétable and, derived from the French, the English word constable. Finally, in Byzantium a marshal with elevated authority, notably a borderlands military command, is also known as an Exarch.
In many countries, the rank of marshal, cf. field marshal, is the highest army rank, outranking other general officers. The equivalent navy rank is often admiral of the fleet.