What is the X in X-mas?
Old English heord "herd, flock," from Proto-Germanic *herdo- (cf. Old Norse hjorð, Old High German herta, German Herde, Gothic hairda "herd"), from PIE *kerdh- "a row, group, herd" (cf. Sanskrit śárdhah "herd, troop," Old Church Slavonic čreda "herd," Greek korthys "heap," Lithuanian kerdžius "shepherd"). Herd instinct in psychology is first recorded 1908.
mid-13c., "to watch over or herd (livestock);" of animals, "to gather in a herd, to form a flock," late 14c., from herd (n.). Related: Herded; herding.
Gen. 13:5; Deut. 7:14. (See CATTLE.)