What is the X in X-mas?
mid-16c., in reference to the ancient philosophy, from Greek kynikos "a follower of Antisthenes," literally "dog-like," from kyon (genitive kynos) "dog" (see canine). Supposedly from the sneering sarcasm of the philosophers, but more likely from Kynosarge "Gray Dog," name of the gymnasium outside ancient Athens (for the use of those who were not pure Athenians) where the founder, Antisthenes (a pupil of Socrates), taught. Diogenes was the most famous. Popular association even in ancient times was "dog-like" (Lucian has kyniskos "a little cynic," literally "puppy"). Meaning "sneering sarcastic person" is from 1590s.