Ghost of dog enthralling most of southern county (7)
I believe the answer is:
phantom
'ghost' is the definition.
(I've seen this before)
'dog enthralling most of southern county' is the wordplay.
'dog' becomes 'pom' (short for Pomeranian).
'enthralling' means one lot of letters goes inside another.
'most of southern county' becomes 'hant' (I am not sure about this - if you are sure you should believe this answer much more).
'pom' going around 'hant' is 'PHANTOM'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for phantom that I've seen before include "Ghost of the Opera" , "Ballet-dancing costume" , "Sightseeing journey" , "Something creepy" , "shadow of his former self?" .)