What is the X in X-mas?
late 14c., from Anglo-French expense, Old French espense "money provided for expenses," from Late Latin expensa "disbursement, outlay, expense," noun use of neuter plural past participle of Latin expendere "to weigh out money, to pay down" (see expend).
Latin spensa also yielded Medieval Latin spe(n)sa, whose sense specialized to "outlay for provisions," then "provisions, food," which was borrowed into Old High German as spisa and is the root of German Speise "food," now mostly meaning prepared food, and speisen "to eat."
1909, from expense (n.). Related: Expensed; expensing.