Welshwoman second of agents subverted (4)
I believe the answer is:
gwen
'welshwoman' is the definition.
Both the definition and answer are singular nouns.
Maybe there's a link between them I don't understand?
'second of agents subverted' is the wordplay.
'second of agents' becomes 'g' (end letter of 'agents').
'subverted' becomes 'wen' (I can't justify this - if you can you should believe this answer much more).
'g'+'wen'='GWEN'
Can you help me to learn more?
(Other definitions for gwen that I've seen before include "name" , "Sister of Augustus John" .)