Sit with a book (4)
I believe the answer is:
read
'sit with a book' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for read that I've seen before include "Interpret writing" , "Study (for a degree?)" , "Studied" , "Check, emend (proof)" , "Undertake a course of study" .)