What is the X in X-mas?
early 13c., "that which is vain, futile, or worthless," from Old French vanite, from Latin vanitatem (nominative vanitas) "emptiness, foolish pride," from vanus "empty, vain, idle" (see vain). Meaning "self-conceited" is attested from mid-14c. Vanity table is attested from 1936. Vanity Fair is from "Pilgrim's Progress" (1678).