Dad backing mum? It's obvious (8)
I believe the answer is:
apparent
'obvious' is the definition.
(similar in meaning)
'dad backing mum?' is the wordplay.
'dad' becomes 'pa' (both can mean one's father).
'backing' shows that the letters should be reversed in order.
'mum?' becomes 'parent' (mum is a kind of parent).
'pa' back-to-front is 'ap'.
'ap'+'parent'='APPARENT'
'it's' acts as a link.
(Other definitions for apparent that I've seen before include "Seeming to be but not necessarily so" , "Obvious, evident" , "See 1" , "Evident, manifest" , "Ostensible, seeming" .)