What is the X in X-mas?
1944, from German Angst "neurotic fear, anxiety, guilt, remorse," from Old High German angust, from the root of anger. George Eliot used it (in German) in 1849, and it was popularized in English by translation of Freud's work, but as a foreign word until 1940s. Old English had a cognate word, angsumnes "anxiety," but it died out.
angst 1 (ängkst)
A feeling of anxiety or apprehension often accompanied by depression.