Small religious ceremony concerned with the soul (9)
I believe the answer is:
spiritual
'concerned with the soul' is the definition.
(spiritual can mean relating to one's soul)
'small religious ceremony' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'religious' becomes 'pi' (old-fashioned term for pious).
'ceremony' becomes 'ritual' (I've seen this before).
's'+'pi'+'ritual'='SPIRITUAL'
(Other definitions for spiritual that I've seen before include "Relating to religious belief" , "Relating to the sacred or the soul" , "lords" , "Relating to the holy or divine" , "Relating to religion" .)