What is the X in X-mas?
"sign or character representing a word," 1840, from Greek logos (see logos) + -gram. Generically, "any symbol representing graphically a product, idea, etc." is from 1966. The earliest use of the word (1820) is in the sense "logograph," but OED explains this as a substitute "for logograph, which in this sense is itself a mistake for logogriph."