Sovereign for stationery item (5)
I believe the answer is:
ruler
I believe this is a double definition.
'sovereign' is the first definition.
(I've seen this before)
'stationery item' is the second definition.
(I've seen this before)
'for' is the link.
(Other definitions for ruler that I've seen before include "It can be used to strike" , "that should go straight" , "Stationery item" , "Strip used in drawing straight lines" , "' - - of the Queen's Navee!'" .)