Power one observed in catty type leading a new church (9)
I believe the answer is:
puissance
'power' is the definition.
(puissance can mean power or influence)
'one observed in catty type leading a new church' is the wordplay.
'one' becomes 'i' (Roman numeral).
'observed in' is an insertion indicator.
'catty type' becomes 'puss' (puss can mean a cat).
'leading' is a charade indicator (letters next to each other).
'a new church' becomes 'ance' (I can't justify this - if you can you should give a lot more credence to this answer).
'i' put inside 'puss' is 'puiss'.
'puiss'+'ance'='PUISSANCE'
Can you help me to learn more?
(Other definitions for puissance that I've seen before include "Power" , "Event with obstacles" , "Test of a horse's ability over large obstacles in showjumping" , "Once might" , "In show-jumping, test of horse's jumping ability" .)