A spirit seen by mansion in Battle (9)
I believe the answer is:
agincourt
'battle' is the definition.
(Agincourt is an example)
'a spirit seen by mansion' is the wordplay.
'spirit' becomes 'gin' (I've seen this before).
'seen by mansion' becomes 'court' (I can't explain this - if you can you should believe this answer much more).
'a'+'gin'+'court'='AGINCOURT'
'in' is the link.
Can you help me to learn more?
(Other definitions for agincourt that I've seen before include "Henry V's battle" , "Battleground" , "English-French battle" , "where Henry met Constable" , "Battle in Hundred Years' War" .)