The second book of the Old Testament (6)
I believe the answer is:
exodus
'the second book of the old testament' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for exodus that I've seen before include "Biblical book - going out" , "Book following Genesis" , "Old Testament Book 2" , "Flight of the Israelites out of Egypt, led by Moses" , "8, Book 2" .)