A mumpsimus is person who clings to something even after it has been shown to be wrong, or the action of clinging to incorrect belief. For example, when someone insists on saying irregardless regardless of the fact it is NOT a word, then that person is a mumpsimus and his act of using the word irregardless is also a mumpsimus. Another example of a mumpsimus adhering to a mumpsimus would be someone who is convinced is the world is 3000 years old.
Mumpsimus: it may be my new favorite word.
Although people do not use this word much nowadays (more is the pity), it was used quite a bit in the educated and/or upper-class in the 16th century:
“In William Tyndale‘s 1530 book Practice of Prelates, the word was used in the sense of a stubborn opponent to Tyndale’s views. He said that the men whom Cardinal Wolsey had asked to find reasons why Catherine of Aragon was not truly the wife of King Henry VIII of England were “…all lawyers, and other doctors, mumpsimuses of divinity”. Henry VIII reportedly said of arguing preachers, “Some are too stiff in their old Mumpsimus, and others too busie and curious in their new Sumpsimus.” Hugh Latimer (1487–1555) used the term in two sermons he preached in 1552, saying: “When my neighbour is taught, and knoweth the truth, and will not believe it, but will abide in his old mumpsimus…” and again: “Some be so obstinate in their old mumpsimus, that they cannot abide the true doctrine of God.”
It was a major piece of snark. If used today, the word mumpsimus would be followed by an “Oh, snap!”.
I really, really want this word to come back into regular usage.