Frankness and love seen in a dog (7)
I believe the answer is:
candour
'frankness' is the definition.
(synonyms)
'and love seen in a dog' is the wordplay.
'love' becomes 'o' (love means zero in tennis).
'seen in' indicates putting letters inside.
'a dog' becomes 'cur' (a cur is an aggressive or scruffy dog).
'and'+'o'='ando'
'ando' put inside 'cur' is 'CANDOUR'.
(Other definitions for candour that I've seen before include "Openness, honesty" , "Opening up" , "'Frankness, honesty (7)'" , "open)" , "telling it like it is" .)