Dining room is a shambles (4)
I believe the answer is:
mess
I believe this clue is a double definition.
'dining room' is the first definition.
(I know that mess is a type of dining room)
'a shambles' is the second definition.
(I've seen this before)
'is' is the link.
(Other definitions for mess that I've seen before include "Mix-up" , "Where soldiers may eat" , "An officer's untidy dining room" , "sloppy > food" , "State of confusion - where servicemen eat" .)