Last book of the Old Testament (7)
I believe the answer is:
malachi
'last book of the old testament' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for malachi that I've seen before include "Biblical prophet" , "Hebrew prophet; OT book" , "8, Book 39" , "Old Testament prophet" , "Part of Bible" .)