ˈməmpsəməs noun
( -es )
Etymology: error for Latin sumpsimus we have taken, 1st plural perfect indicative of sumere to take; from a familiar story in which this error was made in the ritual of the mass by an illiterate priest who when corrected replied that he would not change his old mumpsimus for his critic's new sumpsimus — more at assume
1. : a bigoted adherent to exposed but customary error
2. : a custom or tenet adhered to by a mumpsimus