What is the X in X-mas?
Old English hæsl, hæsel, from Proto-Germanic *hasalaz (cf. Old Norse hasl, Middle Dutch hasel, German hasel), from PIE *koselo- "hazel" (cf. Latin corulus, Old Irish coll "hazel"). Shakespeare ("Romeo and Juliet," 1592) was first to use it (in print) in the sense of "reddish-brown color of eyes" (in reference to the color of ripe hazel-nuts), when Mercutio accuses Benvolio of being testy with:
Thou wilt quarrell with a man for cracking Nuts, hauing no reason, but because thou hast hasell eyes.
Heb. luz, (Gen. 30:37), a nutbearing tree. The Hebrew word is rendered in the Vulgate by amygdalinus, "the almond-tree," which is probably correct. That tree flourishes in Syria.