The most common and most likely answer to this crossword clue is the 12 letter word OBSCURANTIST
I've seen this crossword clue in The Sunday Telegraph
O
B
S
C
U
R
A
N
T
I
S
T
More clues leading to the result OBSCURANTIST
- One making complex subtractions erroneously
- One who makes dim, daft subtractions
- One resisting reforms in biblical texts: curbs upset opponents
- One opposing reforms organized station curbs
- Enlightenment certainly doesn’t come easily from one finding subtractions tricky
- Wrong subtractions standing in the way of enlightenment
- Resisting enlightenment, having messed up subtractions
Buddy explains!

The straight part
We know that "Resisting enlightenment" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case resisting enlightenment = obscurantist.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 OBSCURANTIST mean?
OBSCURANTIST noun- A practitioner of obscurantism; an obscurant