Top dog, say (4)
I believe the answer is:
peak
'top' is the definition.
(synonyms)
'dog say' is the wordplay.
'dog' becomes 'peke' (short for Pekingese).
'say' shows a homophone (sound like).
'peke' is a homophone of 'PEAK'.
(Other definitions for peak that I've seen before include "maximum pitch" , "Mountain top" , "Apex" , "Acme" , "High point" .)