Where those who serve may be served (5)
I believe the answer is:
naafi
'where those who serve may be served' is the definition.
The definition suggests a singular noun which matches the answer.
This is all the clue.
(Other definitions for naafi that I've seen before include "Army canteen/shop" , "Supplier of the Services (acronym)" , "Armed services canteen" , "eatery" , "Caterers" .)