Show anger, but with restraint (6)
I believe the answer is:
bridle
'restraint' is the definition.
(I know that bridle is a type of restraint)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for bridle that I've seen before include "Show resentment" , "Horse restraint" , "A curb; show scorn (at)" , "Rein" , "Restrain" .)