What is the X in X-mas?
Old English halgian "to make holy, to honor as holy, consecrate, ordain," related to halig "holy," from Proto-Germanic *hailaga- (cf. Old Saxon helagon, Middle Dutch heligen, Old Norse helga), from PIE root *kailo- "whole, uninjured, of good omen" (see health). Used in Christian translations to render Latin sanctificare. Also used since Old English as a noun meaning "holy person, saint." Related: Hallowed; hallowing.
to render sacred, to consecrate (Ex. 28:38; 29:1). This word is from the Saxon, and properly means "to make holy." The name of God is "hallowed", i.e., is reverenced as holy (Matt. 6:9).