The most common and most likely answer to this crossword clue is the 6 letter word RESITS
R
E
S
I
T
S
More clues leading to the result RESITS
- Struggle raising temperature on subsequent attempts
- Nun relaxes around middle of confiteor
- Sister screwed up second chances
- Types of exams offering breaks around lunchtime?
- Romeo, alone at last, poses questions to be faced a second time?
- Refuse to turn back in second set of exams
- Stand firm, switching the last two exams
- Model sister appears for exam once again
Buddy explains!

The straight part
We know that "Nun" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case nun = resits.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 RESITS mean?
RESITS noun- An examination taken a second time.