What is the X in X-mas?
c.1300, earlier aghe, c.1200, from a Scandinavian source, e.g. Old Norse agi "fright;" from Proto-Germanic *agiz- (cf. Old English ege "fear," Old High German agiso "fright, terror," Gothic agis "fear, anguish"), from PIE *agh-es- (cf. Greek akhos "pain, grief"), from root *agh- "to be depressed, be afraid" (see ail). Current sense of "dread mixed with veneration" is due to biblical use with reference to the Supreme Being. Awe-inspiring is recorded from 1814.