The first book of the Old Testament (7)
I believe the answer is:
genesis
'the first book of the old testament' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for genesis that I've seen before include "rock group" , "Origin -- see sign (anag)" , "Beginning (in the Bible)" , "Origin; Bible book" , "Bible's first book" .)