On appeal, exam papers may be extraordinary (10)
I believe the answer is:
remarkable
'extraordinary' is the definition.
(similar in meaning)
'on appeal exam papers' is the wordplay.
I cannot quite see how this works, but
'on' could be 're' ('on' can be mean 'with reference to') and 're' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
'may be' is the link.
Can you help me to learn more?
(Other definitions for remarkable that I've seen before include "surprising?" , "Striking" , "Extraordinary" , "Noteworthy" , "unusual" .)