Restrain mother hen (6)
I believe the answer is:
dampen
'restrain' is the definition.
(thesaurus)
'mother hen' is the wordplay.
'mother' becomes 'dam' (female parent of an animal).
'hen' becomes 'pen' (I can't explain this - if you can you should give a lot more credence to this answer).
'dam'+'pen'='DAMPEN'
Can you help me to learn more?
(Other definitions for dampen that I've seen before include "get a bit wet" , "Make moist or depress spirits" , "Apply liquid!" , "Stifle" , "Moisten" .)