Muddle in canteen (4)
I believe the answer is:
mess
This clue is a double definition.
'muddle' is the first definition.
(I know that muddle can be written as mess)
'canteen' is the second definition.
(I've seen this before)
'in' is the link.
(Other definitions for mess that I've seen before include "Disagreeable mixture" , "Food-hall" , "Place to eat" , "terrible state" , "An officer's untidy dining room" .)