
1) Diehard of a sort 2) Notion
Found on
https://www.crosswordclues.com/clue/mumpsimus

1) Flat-earther
Found on
https://www.crosswordclues.com/clue/mumpsimus

A mumpsimus is an action by a person, or the person themselves, who adheres to a routine, idea, custom, set of beliefs, or a certain use of language that has been shown to be unreasonable or incorrect. For example, a person may continue to say all intents and purposes as all intensive purposes, even after being corrected. ==Definition== Mumpsimus ...
Found on
http://en.wikipedia.org/wiki/Mumpsimus

view stubbornly held even when shown to be wrong
Found on
http://phrontistery.info/m.html
noun a traditional notion that is obstinately held although it is unreasonable; `he still holds to the old mumpsimus that a woman`s place is in the kitchen`
Found on
https://www.encyclo.co.uk/local/20974

adherence to or persistence in an erroneous use of language, memorization, practice, belief, etc., out of habit or obstinacy (opposed to sumpsimus). · a person who persists in a mistaken expression or practice (opposed to sumpsimus).
Found on
https://www.infoplease.com/dictionary/mumpsimus
No exact match found.