The most common and most likely answer to this crossword clue is the 11 letter word CREATIONISM
I've seen this crossword clue in The Guardian
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More clues leading to the result CREATIONISM
Buddy explains!
The straight part
We know that "Fundamentalist belie" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fundamentalist belie = creationism.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CREATIONISM mean?
CREATIONISM noun- The Abrahamic doctrine that each individual human soul is created by God, as opposed to traducianism.
- Any creationary belief, especially a belief that the origin of things is due to an event or process of creation brought about by the deliberate act of any divine agency, such as a Creator God (creator god).
- The belief that a deity created the world, especially as described in a particular religious text, such as the Quran or the Book of Genesis.