What is the X in X-mas?
Old English hyrnet, hurnitu "large wasp, beetle," probably from Proto-Germanic *hurz-nut- (cf. Old Saxon hornut, Middle Dutch huersel, Dutch horzel, Old High German hornaz, German Hornisse "hornet"), from PIE imitative (buzzing) root *krs-, as preserved in Old Church Slavonic srusa, Lithuanian szirszu "wasp." On this theory, the English word (as well as German Hornisse) was altered by influence of horn, to suggest either "horner" (from the sting) or "horn-blower" (from the buzz). Cf. also Old Saxon hornobero "hornet," literally "trumpeter."
Heb. tsir'ah, "stinging", (Ex. 23:28; Deut. 7:20; Josh. 24:12). The word is used in these passages as referring to some means by which the Canaanites were to be driven out from before the Israelites. Some have supposed that the word is used in a metaphorical sense as the symbol of some panic which would seize the people as a "terror of God" (Gen. 35:5), the consternation with which God would inspire the Canaanites. In Palestine there are four species of hornets, differing from our hornets, being larger in size, and they are very abundant. They "attack human beings in a very furious manner." "The furious attack of a swarm of hornets drives cattle and horses to madness, and has even caused the death of the animals."