Vault seen in centre of Bavarian church (4)
I believe the answer is:
arch
'vault' is the definition.
(thesaurus)
'centre of bavarian church' is the wordplay.
'centre of' means to look at the middle letters.
'church' becomes 'ch' (common abbreviation).
The centre of 'bavarian' is 'ar'.
'ar'+'ch'='ARCH'
'seen in' acts as a link.
(Other definitions for arch that I've seen before include "Roguish, cunning" , "Teasing; part of foot" , "not to go straight?" , "Vaulted opening" , "Structure with a keystone" .)