Union member's paraphernalia ultimately upset polymath (9)
I believe the answer is:
trousseau
This clue could be a double definition.
'union member's paraphernalia' is the first definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'ultimately upset polymath' is the second definition.
The definition suggests a singular noun which matches the answer.
Can you help me to learn more?
(Other definitions for trousseau that I've seen before include "Union's present" , "Clothes etc. collected by a bride for her marriage" , "New bride's linen, etc" , "Items collected by a bride for her marriage" , "Bridal gear" .)