Apse concerned with church vessel (6)
I believe the answer is:
recess
'apse' is the definition.
(I've seen this before)
'concerned with church vessel' is the wordplay.
'concerned with' becomes 're' (re can mean regarding, concerning).
'church' becomes 'CE' (abbreviation for Church of England).
'vessel' becomes 'SS' (prefix in ship names eg SS Great Britain).
're'+'ce'+'ss'='RECESS'
(Other definitions for recess that I've seen before include "Niche or intermission" , "Temporary cessation from business" , "break needed!" , "Temporary suspension of business" , "take time out" .)