Regulating device (8)
I believe the answer is:
governor
'regulating device' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for governor that I've seen before include "Official in charge of prison" , "Official in charge of town/region" , "Head of each state in the USA" , "Motor control to regulate speed" , "Ron, go rev up the state head" .)