Second book of the Bible (6)
I believe the answer is:
exodus
'second book of the bible' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for exodus that I've seen before include "A great departure as in the Bible" , "Biblical book -- group escape from a hostile environment" , "Biblical book - going out" , "Mass leaving" , "Second book of OT" .)