Stationery item for a sovereign (5)
I believe the answer is:
ruler
I believe this is a double definition.
'stationery item' is the first definition.
(I've seen this before)
'a sovereign' is the second definition.
(I've seen this before)
'for' is the link.
(Other definitions for ruler that I've seen before include "measure applied in school?" , "Emperor - measure" , "Straight edge; governor" , "that should go straight" , "Emperor, maybe" .)