What is the X in X-mas?
1894, "alcoholic drink taken before a meal to stimulate the appetite," from French apéritif "laxative, laxative liqueur," literally "opening," from Latin aperitivus, from aperire "to open" (see overt). Cf. Middle English apertive (adj.), a medical word meaning "capable of opening or dilating" (pores, etc.), early 15c.