Religious leader to talk endlessly (5)
I believe the answer is:
rabbi
'religious leader' is the definition.
(Jewish religious leader)
'talk endlessly' is the wordplay.
'talk' becomes 'rabbit' (rabbit can informally mean to talk).
'endlessly' means to remove the last letter.
'rabbit' with its last letter taken off is 'RABBI'.
'to' is the link.
(Other definitions for rabbi that I've seen before include "A Jewish priest" , "Teacher of Jewish law" , "Jewish religious teacher" , "A Jewish scholar or synagogue leader" , "endless waffle" .)