A small cat and a big dog (5)
I believe the answer is:
akita
'big dog' is the definition.
'a small cat and a' is the wordplay.
'small cat' becomes 'kit'.
'and' is a charade indicator (letters next to each other).
'a'+'kit'+'a'='AKITA'
(Other definitions for akita that I've seen before include "dog from Japan" , "powerful dog" , "Japanese breed of dog" , "heavy brute?" .)