Fake blessing - not half a mess! (8)
I believe the answer is:
shambles
'a mess' is the definition.
(thesaurus)
'fake blessing not half' is the wordplay.
'fake' becomes 'sham' ('sham' can be a synonym of 'fake').
'not half' suggests halving the letters.
'blessing' cut in half is 'bles'.
'sham'+'bles'='SHAMBLES'
(Other definitions for shambles that I've seen before include "utter chaos" , "Slaughterhouse; mess" , "Mediaeval street in York" , "confused situation" , "Scene of slaughter or disorder" .)