To many the three wise men are incredible (5)
I believe the answer is:
magic
'to many' is the definition.
I can't tell whether this defines the answer.
'three wise men are incredible' is the wordplay.
'three wise men' becomes 'magi' (I've seen this in another clue).
'are incredible' becomes 'c' (I can't justify this - if you can you should give a lot more credence to this answer).
'magi'+'c'='MAGIC'
'the' acts as a link.
Can you help me to learn more?
(Other definitions for magic that I've seen before include "Illusory feat" , "Necromancy" , "Art that supposedly invokes supernatural powers" , "Witchcraft" , "Fungus causing trips?" .)