Brilliant books (3)
I believe the answer is:
lit
This clue is a double definition.
'brilliant' is the first definition.
(brilliant can mean shining or lit up)
'books' is the second definition.
(abbreviation for literature)
(Other definitions for lit that I've seen before include "books etc?" , "Burning" , "Illuminated" , "Settled" , "Set fire to" .)