Playwright harbouring love for dog (7)
I believe the answer is:
pointer
'dog' is the definition.
(pointer is a kind of dog)
'playwright harbouring love' is the wordplay.
'playwright' becomes 'pinter' (Harold Pinter).
'harbouring' means one lot of letters goes inside another.
'love' becomes 'o' (In tennis, 'love' means 'zero').
'pinter' enclosing 'o' is 'POINTER'.
'for' acts as a link.
(Other definitions for pointer that I've seen before include "Tip; dog" , "something moved by mouse" , "Dog < or horse or" , "helpful tip!" , "under control of mouse" .)