Quibble about it being put in favourite pea soup? (8)
I believe the answer is:
pettifog
'quibble' is the definition.
(synonyms)
'about it being put in favourite pea soup?' is the wordplay.
'about' says the letters should be written backwards.
'being put in' means one lot of letters goes inside another.
'favourite' becomes 'pet' (synonyms).
'pea soup?' becomes 'fog' (pea soup is a kind of fog).
'it' in reverse letter order is 'ti'.
'pet'+'fog'='petfog'
'ti' put inside 'petfog' is 'PETTIFOG'.
(Other definitions for pettifog that I've seen before include "Quibble as lawyers" , "trifle" , "Raise absurd objection" .)