What is the X in X-mas?
late 13c., from Old French fieu, fief "fief, possession, holding, domain; feudal duties, payment," from Medieval Latin feodum "land or other property whose use is granted in return for service," widely said to be from Frankish *fehu-od "payment-estate," or a similar Germanic compound, in which the first element is cognate with Old English feoh "money, movable property, cattle" (also German Vieh "cattle," Gothic faihu "money, fortune"), from PIE *peku- "cattle" (cf. Sanskrit pasu, Lithuanian pekus "cattle;" Latin pecu "cattle," pecunia "money, property"); second element similar to Old English ead "wealth."
OED rejects this, and suggests a simple adaptation of Germanic fehu, leaving the Medieval Latin -d- unexplained. Sense of "payment for services" first recorded late 14c. Fee-simple is "absolute ownership," as opposed to fee-tail "entailed ownership," inheritance limited to some particular class of heirs (second element from Old French taillir "to cut, to limit").
in feudal English law, an interest in land bound up inalienably in the grantee and then forever to his direct descendants. A basic condition of entail was that if the grantee died without direct descendants the land reverted to the grantor. The concept, feudal in origin, supported a landed aristocracy because it served to prevent the disintegration of large estates through divisible inheritance or the lack of heirs. Statutory reforms in England now permit the owner to convey the entailed land by a simple deed and even by will