diehard

What it means

1. idiomaticUnreasonably or stubbornly resisting change.
2. idiomaticFanatically opposing progress or reform.
3. idiomaticComplete; having no opposite opinion of anything in a particular topic of one's values; thorough of in one's beliefs.

   For a Roman Catholic teacher, he sure is a diehard fundamentalist.

   1 more example

   The libertarian right of the Consservative Party, many of them diehard Europhobes, privately referred to the health minister and his advisers as "the Gestapo" for their faith in enforced lockdowns.

   2022, Ian McEwan, Lessons, page 644

In a sentence

For a Roman Catholic teacher, he sure is a diehard fundamentalist.

Where it comes from

Deverbal from die hard.