What is the X in X-mas?
late 15c. "body size" (either large or small, with adjective), from Old French corpulence (14c.) "corpulence; physical size, build," from Latin corpulentia "grossness of body," noun of quality from corpulentus (see corpulent). Restriction to "bulkiness, obesity" began late 16c. Related: Corpulency.
corpulence cor·pu·lence (kôr'pyə-ləns)
The condition of being excessively fat; obesity.