A French religious man has one loosened (5)
I believe the answer is:
undid
'loosened' is the definition.
(I've seen this before)
'a french religious man has one' is the wordplay.
'a french' becomes 'un' ('a' in French).
'religious man' becomes 'DD' (abbreviation for Doctor of Divinity degree).
'has' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral).
'dd' placed around 'i' is 'did'.
'un'+'did'='UNDID'
(Other definitions for undid that I've seen before include "Cancelled - destroyed" , "Loosened; ruined" , "Released" , "Cancelled, reversed (an action)" , "solved knotty problem" .)