Key books in religious studies: his speciality? (5)
I believe the answer is:
rabbi
'studies his speciality?' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'key books in religious' is the wordplay.
'key' becomes 'A' (musical key).
'books' becomes 'BB' (an abbreviation for book written twice).
'in' is an insertion indicator.
'religious' becomes 'ri' (I can't explain this - if you can you should believe this answer much more).
'a'+'bb'='abb'
'abb' going within 'ri' is 'RABBI'.
Can you help me to learn more?
(Other definitions for rabbi that I've seen before include "Religious leader in a Jewish community" , "Hebrew teacher" , "Jewish religious teacher" , "Religious leader of Jewish congregation" , "Jewish learned man" .)