What is the X in X-mas?
Old English fær "journey, road, passage, expedition," strong neuter of faran "to journey" (see fare (v.)); merged with faru "journey, expedition, companions, baggage," strong fem. of faran. Original sense is obsolete, except in compounds (wayfarer, sea-faring, etc.) Meaning "food provided" is c.1200; that of "conveyance" appears in Scottish early 15c. and led to sense of "payment for passage" (1510s).
Old English faran "to journey, set forth, go, travel, wander, get on, undergo, make one's way," from Proto-Germanic *faranan (cf. Old Saxon, Old High German, Gothic faran, Old Norse and Old Frisian fara, Dutch varen, German fahren), from PIE *por- "going, passage," from root *per- (2) "to lead, pass over" (see port (n.1)). Related: Fared; faring.