Definition from Wiktionary, the free dictionary
From the idiom "to die hard".
- Unreasonably or stubbornly resisting change.
- Fanatically opposing progress or reform.
- Complete; 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.
- See also Wikisaurus:obstinate
diehard (plural diehards)
- A person with such an attitude.