Old transformer St Michael transformed (9)
I believe the answer is:
alchemist
'old transformer' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'st michael transformed' is the wordplay.
'transformed' indicates an anagram.
'st'+'michael'='stmichael'
'stmichael' anagrammed gives 'ALCHEMIST'.
Can you help me to learn more?
(Other definitions for alchemist that I've seen before include "St Michael in role of one turning base metal into gold" , "magician" , "Seeker after gold" , "One tried to turn ordinary metal into gold" , "Early experimenter" .)