Over for a sandwich (5)
I believe the answer is:
round
This clue is a double definition.
'over' is the first definition.
(thesaurus)
'sandwich' is the second definition.
(as in a round of sandwiches)
'for a' is the link.
(Other definitions for round that I've seen before include "Description of Tweedledum" , "A single shot" , "Drinks order" , "toast" , "Approximate" .)