Get lost in a book (4)
I believe the answer is:
read
'get lost in 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 "Use a book" , "See - peruse - understand" , "Absorbed (written text)" , "Undertake a course of study" , "Stomach" .)