In my opinion, a scholarly book? (4)
I believe the answer is:
tome
I believe this is a double definition.
'in my opinion' is the first definition.
(to me)
'a scholarly book?' is the second definition.
(I've seen this before)
(Other definitions for tome that I've seen before include "Large scholarly volume" , "A hefty book" , "dictionary?" , "Large, weighty book" , "Hefty volume" .)