Member of clergy one’s seen in church (8)
I believe the answer is:
minister
'member of clergy' is the definition.
'minister' can be an answer for 'member' (I have seen 'Member of parliament' mean 'minister' so perhaps 'member' could also mean 'minister'). I'm not sure about the 'of clergy' bit.
'one's seen in church' is the wordplay.
'one' becomes 'i' (Roman numeral).
'seen in' is an insertion indicator.
'church' becomes 'minster' (minster is a kind of church).
'i' put inside 'minster' is 'MINISTER'.
Can you help me to learn more?
(Other definitions for minister that I've seen before include "Cabinet member" , "Churchman" , "Form of address" , "Merit sin (anag.)" , "Servant of state or church" .)