Restraining device to exert sovereign control, we hear (4)

I believe the answer is:

rein

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'restraining device to exert sovereign' is the definition.
I can't tell whether this defines the answer.

'control we hear' is the wordplay.
'control' becomes 'reign' (reign is a kind of control).
'we hear' shows a homophone (sound like).
'reign' sounds like 'REIN'.

Can you help me to learn more?

(Other definitions for rein that I've seen before include "Horse's steering strap" , "Slow-up" , "Hold back" , "Controlling strap" , "given free to experienced riders?" .)

I've seen this clue in The Irish News.

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