Bill of fare that’s united soldiers at the front (4)
I believe the answer is:
menu
'bill of fare' is the definition.
(synonyms)
'united soldiers at the front' is the wordplay.
'united' becomes 'u'.
'soldiers' becomes 'men' (I've seen this before).
'at the front' means one lot of letters go next to another.
'u' put after 'men' is 'MENU'.
'that's' acts as a link.
(Other definitions for menu that I've seen before include "Card" , "Choice of dishes" , "Restaurant's list" , "List of dishes on offer" , "restaurant guide" .)