Fish is covered in cream after gutting error (8)
I believe the answer is:
solecism
'error' is the definition.
(solecism is a kind of error)
'fish is covered in cream after gutting' is the wordplay.
'fish' becomes 'sole' (sole is a kind of fish**).
'covered in' is an insertion indicator.
'after gutting' means to remove the middle letters (to gut something is to remove its insides).
'cream' with its middle removed is 'cm'.
'is' inserted into 'cm' is 'cism'.
'sole'+'cism'='SOLECISM'
(Other definitions for solecism that I've seen before include "Faux pas" , "Grammatical mistake" , "Incongruity" , "Error in grammar or manners" , "Grammatical (or social) blunder" .)