Agents seizing church roughly (5)
I believe the answer is:
circa
'roughly' is the definition.
(I've seen this before)
'agents seizing church' is the wordplay.
'agents' becomes 'CIA' (Central Intelligence Agency).
'seizing' indicates putting letters inside (inserted letters are seized).
'church' becomes 'RC' (abbreviation for Roman Catholic).
'cia' enclosing 'rc' is 'CIRCA'.
(Other definitions for circa that I've seen before include "Roughly" , "Approximately (of a year)" , "Approximately (Latin)" , "Preceding a date, this means about" , "About (a time)" .)