Trainee priest welcomes four for healing (8)
I believe the answer is:
curative
'for healing' is the definition.
(synonyms)
'trainee priest welcomes four' is the wordplay.
'trainee priest' becomes 'curate' (I can't explain this - if you can you should believe this answer much more).
'welcomes' is an insertion indicator (in sense of 'invites in').
'four' becomes 'IV' (Roman numerals).
'curate' going around 'iv' is 'CURATIVE'.
Can you help me to learn more?
(Other definitions for curative that I've seen before include "Therapeutic" , "Restoring to health" , "Healing" , "health-giving" , "Medicine" .)