Initially clerics live out, heading away from sister’s convent life (8)
I believe the answer is:
cloister
'convent life' is the definition.
(cloister can mean life in a convent or mastery)
'initially clerics live out heading away from sister's' is the wordplay.
'initially' suggests taking the first letters.
'heading away from' means to remove the first letter.
The initial letters of 'clerics live out' is 'clo'.
'sister' with its first letter taken away is 'ister'.
'clo'+'ister'='CLOISTER'
(Other definitions for cloister that I've seen before include "Covered walkway around courtyard" , "'Religious retreat, a convent, say (8)'" , "Monastic life" , "Cathedral's covered walk" , "ambulatory" .)