Sovereign's piece of stationery (5)
I believe the answer is:
ruler
This could be a double definition.
'sovereign's' is the first definition.
(I've seen this in another clue)
'piece of stationery' is the second definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps there's a link between them I don't understand?
Can you help me to learn more?
(Other definitions for ruler that I've seen before include "Sovereign, for example" , "Aid to drawing straight lines" , "Drawing stick or monarch" , "Straight edge; governor" , "One measures" .)