Muddle in dining-room (4)
I believe the answer is:
mess
I believe this clue is a double definition.
'muddle' is the first definition.
(I know that muddle can be written as mess)
'dining-room' is the second definition.
(I know that mess is a type of dining room)
'in' acts as a link.
(Other definitions for mess that I've seen before include "Army dining room" , "Military dining room" , "pickle" , "Mix-up" , "dish" .)