Expression of revulsion in one heavily criticising carnage (9)
I believe the answer is:
slaughter
'carnage' is the definition.
(I know that carnage can be written as slaughter)
'expression of revulsion in one heavily criticising' is the wordplay.
'expression of revulsion' becomes 'ugh' (expression of disgust).
'in' means one lot of letters goes inside another.
'one heavily criticising' becomes 'slater' (to slate something is to criticise it heavily).
'ugh' going within 'slater' is 'SLAUGHTER'.
(Other definitions for slaughter that I've seen before include "Widespread killing" , "Glare thus to cause bloodthirsty killing" , "Murder" , "Kill cruelly" , "Kill (animals) for food" .)