What is the X in X-mas?
mid-15c., "to bring together," frequentative of Middle English myngen "to mix," from Old English mengan (related to second element in among), from Proto-Germanic *mangjan "to knead together" (cf. Old Saxon mengian, Old Norse menga, Old Frisian mendza, German mengen), from PIE *mag- "to knead, fashion, fit" (see macerate). The formation may have been suggested by cognate Middle Dutch mengelen. Of persons, "to join with others, be sociable" (intransitive), from c.1600. Related: Mingled; mingling.