On appeal, this could prove tedious (10)
I believe the answer is:
repetition
'this could prove tedious' is the definition.
'on appeal' is the wordplay.
'on' becomes 're' ('on' can be mean 'with reference to'**).
'appeal' becomes 'petition' (I've seen this before).
're'+'petition'='REPETITION'
(Other definitions for repetition that I've seen before include "It may result in another hearing" , "saying again and again!" , "Reiteration" , "that offers nothing new?" .)