The dining room is a shambles (4)
I believe the answer is:
mess
I believe this is a double definition.
'the dining room' is the first definition.
(mess is a kind of dining room)
'a shambles' is the second definition.
(I've seen this in another clue)
'is' acts as a link.
(Other definitions for mess that I've seen before include "Chaos, confusion" , "State of confusion - where servicemen eat" , "Untidy muddle" , "Eating place" , "dish" .)