Parting making petty distinctions (4-9)
I believe the answer is:
hair-splitting
'making petty distinctions' is the definition.
(I've seen this before)
'parting' is the wordplay.
I cannot quite see how this works, but
'parting' could be 'splitting' ('split' can be a synonym of 'part') and 'splitting' is found in the answer.
The remaining letters 'hair' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for hair-splitting that I've seen before include "Occupied with petty distinctions" , "Making trivial distinctions" , "Making of petty distinctions" , "Pedantry" .)