What is the X in X-mas?
Greek, literally "fault, failure, guilt," from hamartanein "to fail of one's purpose; to err, sin," originally "to miss the mark."
hamartia ha·mar·ti·a (hä'mär-tē'ə, hə-mär'shē-ə)
A developmental defect characterized by the abnormal arrangement or combination of tissues normally present in a specific area.
((hamartia from Greek hamartanein, "to err"), inherent defect or shortcoming in the hero of a tragedy, who is in other respects a superior being favoured by fortune.