/mump"seuh meuhs/ , n. , pl. mumpsimuses for 2.
1. adherence to or persistence in an erroneous use of language, memorization, practice, belief, etc., out of habit or obstinacy (opposed to sumpsimus ).
2. a person who persists in a mistaken expression or practice (opposed to sumpsimus ).
[ 1520-30; from a story, which perh. originated with Erasmus, of an illiterate priest who said mumpsimus rather than sumpsimus (1st pl. perfect indic. of L sumere to pick up; see CONSUME) while reciting the liturgy, and refused to change the word when corrected ]