mumpsimus

Etymology
Malapropism of, form of , from a story of an old monk who misrecited the with quod in ōre mumpsimus instead of quod in ōre sumpsimus “which we have taken into the mouth”, and stubbornly continued using the incorrect form even after being corrected. Attested 1530 in The Practice of Prelates by, variously attributed to (1517) or.

Noun

 * 1) A person who obstinately adheres to old ways in spite of clear evidence that they are wrong; an ignorant and bigoted opponent of reform.
 * 2) An obvious error that is obstinately repeated despite correction.