A quiet force in religious retreat (6)
I believe the answer is:
ashram
'religious retreat' is the definition.
(I've seen this before)
'a quiet force' is the wordplay.
'quiet' becomes 'sh'.
'force' becomes 'ram' ('ram' can be a synonym of 'force'**).
'a'+'sh'+'ram'='ASHRAM'
'in' acts as a link.
(Other definitions for ashram that I've seen before include "Hindu retreat house" , "religious community" , "Indian hermitage" , "Hindu hermitage" , "Hindu religious retreat" .)