Religious leader to chatter endlessly (5)
I believe the answer is:
rabbi
'religious leader' is the definition.
(Jewish religious leader)
'chatter endlessly' is the wordplay.
'chatter' becomes 'rabbit' (both can mean to talk excessively).
'endlessly' means to remove the last letter.
'rabbit' with its final letter removed is 'RABBI'.
'to' acts as a link.
(Other definitions for rabbi that I've seen before include "Religious person" , "Leader of worshippers" , "legal scholar" , "Jewish minister" , "Religious scholar" .)