Afraid to bring up a bully who's beyond reproach (6,3)
I believe the answer is:
sacred cow
'beyond reproach' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'afraid to bring up a bully' is the wordplay.
I cannot quite see how this works, but
'a' is present in the answer.
'bully' could be 'cow' (cow can mean to bully or oppress) and 'cow' is found within the answer.
This explanation may well be incorrect...
'who's' is the link.
Can you help me to learn more?
(Other definitions for sacred cow that I've seen before include "Person or institution held to be above criticism" , "Object of irrational veneration" , "One unreasonably held to be above criticism" , "Facing this, carp not" , "Object beyond criticism" .)