Dogs, mum's pets (8)
I believe the answer is:
mastiffs
'dogs' is the definition.
(mastiff is a kind of dog)
'mum's pets' is the wordplay.
'mum's' becomes 'mas' ('ma' can be a synonym of 'mum').
'pets' becomes 'tiffs' (I can't explain this - if you can you should give a lot more credence to this answer).
'mas'+'tiffs'='MASTIFFS'
Can you help me to learn more?
(Other definitions for mastiffs that I've seen before include "man's best friends?" , "Powerful deep-chested dogs" .)