Cat with nine tails and domestic dog? (7)
I believe the answer is:
whippet
'domestic dog?' is the definition.
(whippet is a kind of domestic dog)
'cat with nine tails' is the wordplay.
'cat' becomes 'whip' (cat o' nine tails or cat is a type of whip).
'with nine tails' becomes 'pet' (I can't justify this - if you can you should give a lot more credence to this answer).
'whip'+'pet'='WHIPPET'
'and' is the link.
Can you help me to learn more?
(Other definitions for whippet that I've seen before include "Racing-dog" , "Greyhound relative" , "Small greyhound-type dog" , "Fast runner" , "Dog similar to a greyhound" .)