Pious figure clothed in most suitable room? (6)
I believe the answer is:
vestry
'room?' is the definition.
(vestry is a kind of room)
'pious figure clothed in most suitable' is the wordplay.
'pious figure' becomes 'st' (abbreviation for saint).
'clothed in' is an insertion indicator.
'most suitable' becomes 'very' (as in phrases like 'the very thing').
'st' inserted within 'very' is 'VESTRY'.
(Other definitions for vestry that I've seen before include "Parochial meeting-room in church" , "Church changing room" , "meeting of parishioners" , "Part of church used as an office" , "Small room attached to church" .)