Show disapproval of restraint? (6)

I believe the answer is:

bridle

I'm a little stuck... Click here to teach me more about this clue!

'restraint?' is the definition.
(I know that bridle is a type of restraint)

I cannot understand how the remainder of the clue works.

(Other definitions for bridle that I've seen before include "Show indignation" , "Rein" , "Check" , "Become indignant" , "Take offence" .)

I've seen this clue in the Evening Standard.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.