What is the X in X-mas?
French, "name" (9c.), from Latin nomen (see name (n.)). Used in various phrases, e.g. nom de guerre (1670s), name used by a person engaged in some action, literally "war name;" nom de plume (1823), literally "pen name;" nom de théâtre (1874) "stage name." "Nom de plume is open to the criticism that it is ridiculous for English writers to use a French phrase that does not come from France" [Fowler].