Grey looking, like a chook (5)
I believe the answer is:
ashen
'grey looking' is the definition.
'ashen' can be an answer for 'grey' (I've seen this before). I am unsure of the 'looking' bit.
'a chook' is the wordplay.
'chook' becomes 'shen' (I can't justify this - if you can you should give a lot more credence to this answer).
'a'+'shen'='ASHEN'
'like' acts as a link.
Can you help me to learn more?
(Other definitions for ashen that I've seen before include "showing signs of anaemia" , "pale in colour" , "Visibly shocked" , "(Of face) pale (with shock)" , "Like bird" .)