Setter perhaps so exhausted? (3-5)
I believe the answer is:
dog-tired
'exhausted?' is the definition.
(I know that exhausted can be written as dog-tired)
'setter perhaps' is the wordplay.
'setter' becomes 'dog' (a setter is a type of dog).
'perhaps' becomes 'tired' (I can't justify this - if you can you should give a lot more credence to this answer).
'dog'+'tired'='DOG-TIRED'
'so' acts as a link.
Can you help me to learn more?
(Other definitions for dog-tired that I've seen before include "Exhausted" , "Extremely weary" , "Worn out" .)