Dog is a clue (7)
I believe the answer is:
pointer
I believe this is a double definition.
'dog' is the first definition.
(I know that pointer is a type of gun dog)
'a clue' is the second definition.
(thesaurus)
'is' acts as a link.
(Other definitions for pointer that I've seen before include "helpful tip!" , "Game dog, used for its ability to scent" , "Arrow" , "Suggestion" , "under control of mouse" .)