What is the X in X-mas?
"harass," 1918, from alternative form of chevy (1830) "to chase," from a noun chevy (1824, also used as a hunting cry, c.1785), from chevy chase "a running pursuit," probably from the "Ballad of Chevy Chase," popular song from 15c. describing a hunting party on the borderland that turned into a battle between the English and the Scots (the incident probably late 14c.). The place is probably originally Cheviot Chase.
The old song of Chevy-Chase is the favourite ballad of the common people of England, and Ben Jonson used to say, he had rather have been the author of it than of all his works. [Addison, "spectator" No. 70, May 21, 1711]