English playwright keeping old dog (7)
I believe the answer is:
pointer
'old dog' is the definition.
'pointer' can be an answer for 'dog' (pointer is a kind of dog). I am not certain of the 'old' bit.
'english playwright keeping' is the wordplay.
'english' becomes 'o' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'playwright' becomes 'pinter' (Harold Pinter).
'keeping' indicates putting letters inside (some letters kept inside).
'o' placed within 'pinter' is 'POINTER'.
Can you help me to learn more?
(Other definitions for pointer that I've seen before include "Suggestion" , "Arrow" , "Tip; dog" , "Indicator" , "Dog; cursor" .)