Dog duke kept in south coast resort (6)
I believe the answer is:
poodle
'dog' is the definition.
(poodle is a kind of dog)
'duke kept in south coast resort' is the wordplay.
'duke' becomes 'd'.
'kept in' means one lot of letters goes inside another.
'south coast resort' becomes 'poole'.
'd' going into 'poole' is 'POODLE'.
(Other definitions for poodle that I've seen before include "Servile person; dog" , "Pet dog with clipped curly coat" , "National dog of France?" , "Pet dog; obsequious chap" , "Curly-coated dog" .)