The words 'subject' and 'sovereign' are identical correlatives, whose meaning is combined in the single word 'citizen'.
Gist of Idea
A citizen is a subject who is also sovereign
Jean-Jacques Rousseau (The Social Contract (tr Cress) , III.13)
'Citizen' was the favourite post-revolutionary label, probably based on this remark. I've heard foreigners tease Britons for being 'subjects' of the monarch, where they are pure citizens. But we are all subject to the law, made by others.
Rousseau,Jean-Jacques: 'The Basic Political Writings', ed/tr. Cress,Donald A. [Hackett 1987], p.196