Murphy is fed up seeing parts being returned (4)
I believe the answer is:
spud
'murphy' is the definition.
(synonyms)
'fed up seeing parts being returned' is the wordplay.
'fed' means one lot of letters goes inside another (one word is 'fed' to another).
'seeing parts' says to take the initial letters (I've seen 'part' mean this).
'being' becomes 'dps' (I can't explain this - if you can you should give a lot more credence to this answer).
'returned' says the letters should be written backwards.
The initial letter of 'up' is 'u'.
'u' inserted inside 'dps' is 'dups'.
'dups' back-to-front is 'SPUD'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for spud that I've seen before include "One could be in jacket" , "Tater" , "Charlotte perhaps" , "Tattie" , "short, stocky person" .)