Dad's top favourite! (7)
I believe the answer is:
popular
'favourite' is the definition.
(similar in meaning)
'dad's top' is the wordplay.
I cannot quite understand how this works, but
'dad' could be 'pop' (synonyms) and 'pop' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for popular that I've seen before include "Widely admired" , "appealing to the public" , "Liked or admired by many" , "Commonly known" , "In general favour" .)