Priest changed in spirit (6)
I believe the answer is:
sprite
'spirit' is the definition.
(thesaurus)
'priest changed' is the wordplay.
'changed' indicates anagramming the letters.
'priest' anagrammed gives 'SPRITE'.
'in' is the link.
(Other definitions for sprite that I've seen before include "water pixie" , "A fairy or goblin" , "Brownie" , "Small, playful fairy" , "Puck, say" .)