Wise men join spies with new illusionist (8)
I believe the answer is:
magician
'illusionist' is the definition.
(synonyms)
'wise men join spies with new' is the wordplay.
'wise men' becomes 'magi' (the three wise men from the nativity).
'join' says to put letters next to each other.
'spies' becomes 'cia' (Central Intelligence Agency).
'with' means one lot of letters go next to another.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'magi'+'cia'+'n'='MAGICIAN'
(Other definitions for magician that I've seen before include "Stage conjurer or maker of legerdemain" , "trickster" , "Conjurer, illusionist" , "Conjuror, illusionist" , "Prestidigitator" .)