A mumpsimus (/ˈmʌmpsɪməs/ MUHMP-sih-məs) is a "traditional custom obstinately adhered to however unreasonable it may be",[1] or "someone who obstinately clings to an error, bad habit or prejudice, even after the foible has been exposed and the person humiliated; also, any error, bad habit, or prejudice clung to in this fashion".[2] The term originates in the story of a priest using the nonsense word mumpsimus instead of the Latin sumpsimus when giving mass, and refusing to be corrected on the matter. The word may refer to either the speaker or their habit.
Over time, the contrasting term sumpsimus came into use. To Henry VIII, a sumpsimus is a correction that is unnecessarily litigious or argumentative, but John Burgon used the term for corrections that may be good but are not as important as others.