Mass departure (6)
I believe the answer is:
exodus
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">mass departure</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for exodus that I've seen before include "Mass departure as in Old Testament's second Book" , "8, Book 2" , "Second book of OT" , "Mass departure of people as of Jews from Egypt" , "Book following Genesis" .)