Scholar of Burns, mostly (5)
I believe the answer is:
rabbi
'scholar' is the definition.
(I've seen this before)
'burns mostly' is the wordplay.
'burns' becomes 'rabbie' (poet Robert Burns, nicknamed Rabbie).
'mostly' means to remove the last letter.
'rabbie' with its last letter taken away is 'RABBI'.
'of' acts as a link.
(Other definitions for rabbi that I've seen before include "Minister of a synagogue" , "Jewish law expounder" , "Legal expert" , "Jewish minister" , "A Jewish clergyman" .)