A union man? (6)
I believe the answer is:
joiner
'a union man?' is the definition.
The definition and answer can be both people as well as being singular nouns.
Maybe there's a link between them I don't understand?
'union man?' is the wordplay.
'union' becomes 'join' (synonyms).
'man?' becomes 'er' (I can't justify this - if you can you should believe this answer much more).
'join'+'er'='JOINER'
Can you help me to learn more?
(Other definitions for joiner that I've seen before include "Skilled woodworker" , "Furniture maker" , "Person who makes finished woodwork" , "Carpenter" , "Saw user maybe" .)