mumpsimus |ˈməmpsiməs|noun ( pl. -muses)a traditional custom or notion adhered to although shown to be unreasonable.• a person who obstinately adheres to such a custom or notion.ORIGIN mid 16th cent.: erroneously for Latin sumpsimus in quod in ore sumpsimus ‘which we have taken into the mouth’ (Eucharist), in a story of an illiterate priest who, when corrected, replied “I will not change my old mumpsimus for your newsumpsimus.”
This word is too cool for...words. I'd love to use it, but people would think I'm making up stuff.