Mushy prune eaten by operative (6)
I believe the answer is:
sloppy
'mushy' is the definition.
(thesaurus)
'prune eaten by operative' is the wordplay.
'prune' becomes 'lop' (synonyms).
'eaten by' means one lot of letters goes inside another.
'operative' becomes 'spy' (I've seen this in another clue).
'lop' placed within 'spy' is 'SLOPPY'.
(Other definitions for sloppy that I've seen before include "Careless and messy" , "Slipshod" , "'Careless, shoddy (6)'" , "maudlin" , "Romantic" .)