Dog always following poor Terri (9)
I believe the answer is:
retriever
'dog' is the definition.
(eg a Golden Retriever)
'always following poor terri' is the wordplay.
'always' becomes 'ever' (synonyms).
'following' says to put letters next to each other.
'poor' indicates an anagram.
'terri' with letters rearranged gives 'retri'.
'ever' put after 'retri' is 'RETRIEVER'.
(Other definitions for retriever that I've seen before include "Dog bred to fetch game" , "Dog that fetches for its master" , "Large hunting 11" , "Breed of dog" , "making a complete recovery?" .)