Turn away disheartened assistant covering upstanding cleric (5)
I believe the answer is:
avert
'turn away' is the definition.
(synonyms)
'disheartened assistant covering upstanding cleric' is the wordplay.
'disheartened' says to hollow out the word (remove centre letters) (the middle or heart is removed).
'covering' is an insertion indicator.
'upstanding' says the letters should be written in reverse.
'cleric' becomes 'Rev' (abbreviation for Reverend).
'assistant' with its middle taken out is 'at'.
'rev' back-to-front is 'ver'.
'at' enclosing 'ver' is 'AVERT'.
(Other definitions for avert that I've seen before include "Ward off, deflect" , "Prevent from occurring" , "Ward off (bad event)" , "Prevent from happening" , "Turn aside or ward off" .)