Book ban rescinded by one leader of congregation (5)
I believe the answer is:
rabbi
'leader of congregation' is the definition.
'book ban rescinded by one' is the wordplay.
'book' becomes 'b'.
'ban' becomes 'bar' (I've seen this before).
'rescinded' says the letters should be written in reverse (rescind can mean to take back).
'by' means one lot of letters go next to another.
'one' becomes 'i' (Roman numeral).
'bar' reversed gives 'rab'.
'b' after 'rab' is 'rabb'.
'rabb'+'i'='RABBI'
(Other definitions for rabbi that I've seen before include "legal scholar" , "endless waffle" , "Jewish learned man" , "Sacks, for example" , "Religious leader in a Jewish community" .)