What is the X in X-mas?
"representing vocal sounds," 1803, from Modern Latin phoneticus (1797), from Greek phonetikos "vocal," from phonetos "to be spoken, utterable," verbal adjective of phonein "to speak clearly, utter," from phone "sound, voice" (see fame (n.)).
phonetic pho·net·ic (fə-nět'ĭk)
Of or relating to phonetics.
Representing the sounds of speech with a set of distinct symbols, each designating a single sound.