Relating to a sovereign (5)
I believe the answer is:
royal
'relating to a sovereign' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for royal that I've seen before include "Referring to the sovereign" , "Old gold coin -- stag with 12 or more points" , "Excellent" , "Wills, perhaps" , "Relating to a monarch" .)