What is the X in X-mas?
c.1300, "to fester," from Old French rancler, earlier raoncler, draoncler "to suppurate, run," from draoncle "abscess, festering sore," from Medieval Latin dracunculus, literally "little dragon," diminutive of Latin draco "serpent, dragon" (see dragon). The notion is of an ulcer caused by a snake's bite. Meaning "cause to fester" is from c.1400. Related: Rankled; rankling.