Bishop indulged in beer to get rotten (5)
I believe the answer is:
addle
'get rotten' is the definition.
(I've seen this before)
'bishop indulged in beer' is the wordplay.
I cannot quite see how this works, but
'bishop' could be 'dd' (DD stands for Doctor of Divinity) and 'dd' is located in the answer.
'beer' could be 'ale' (type of beer) and 'ale' is located in the leftover letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'to' acts as a link.
Can you help me to learn more?
(Other definitions for addle that I've seen before include "(Of eggs) turn bad" , "Confuse - decay" , "Get rotten" , "Go rotten" , "Befuddle" .)