The word seneschal can have several different meanings, all of which reflect certain types of supervising or administering in a historic context. Most commonly, a seneschal was a senior position filled by a court appointment within a royal, ducal, or noble household during the Middle Ages and early Modern period - historically a steward or majordomo of a medieval great house. In a medieval royal household, a seneschal was in charge of domestic arrangements and the administration of servants, which, in the medieval period particularly, meant the seneschal might oversee hundreds of laborers, servants and their associated responsibilities, and have a great deal of power in the community, at a time when much of the local economy was often based on the wealth and responsibilities of such a household.
A second meaning is more specific, and concerns the late medieval and early modern nation of France, wherein the seneschal (French: sénéchal) was also a royal officer in charge of justice and control of the administration of certain southern provinces called seneschalties, holding a role equivalent to a northern French bailiff (bailli).
Finally, in the United Kingdom primarily, seneschal is an ecclesiastical term, referring to a cathedral official.
The term, first attested in 1350-1400, was borrowed from Anglo-Norman seneschal "steward", from Old Dutch *siniscalc "senior retainer" (attested in Latin siniscalcus (692 AD), Old High German senescalh), a compound of *sini- (cf. Gothic sineigs "old", sinista "oldest") and scalc "servant", ultimately a calque of Late Latin senior scholaris "senior guard".
The scholae in the late Roman Empire referred to the imperial guard, divided into senior (seniores) and junior (juniores) units. The captain of the guard was known as comes scholarum. When Germanic tribes took over the Empire, the scholae were merged or replaced with the Germanic king's warband (cf. Vulgar Latin *dructis, OHG truht, Old English dryht) whose members also had duties in their lord's household like a royal retinue. The king's chief warbandman and retainer (cf. Old Saxon druhting, OHG truhting, truhtigomo OE dryhtguma, dryhtealdor), from the 5th century on, personally attended on the king, as specifically stated in the Codex Theodosianus of 413 (Cod. Theod. VI. 13. 1; known as comes scholae). The warband, once sedentary, became first the king's royal household, and then his great officers of state, and in both cases the seneschal is synonymous with steward.
In late medieval and early modern France, the seneschal was originally a royal steward overseeing the entire country but developed into an agent of the crown charged with administration of a seneschalty (French: sénéchaussée), one of the districts of the crown lands in Languedoc and Normandy. Hallam states that the first seneschals to govern in this manner did so by an 1190 edict of Philip II. The seneschals also served as the chief justice of the royal courts in their areas.
Under rulers of England
The dictionary definition of seneschal at Wiktionary