Old Testament book characters (7)
I believe the answer is:
numbers
This clue is a double definition.
'old testament book' is the first definition.
(I've seen this before)
'characters' is the second definition.
(number is a type of symbol or character)
(Other definitions for numbers that I've seen before include "which may knock you out?" , "Ciphers" , "Fourth OT book - figures" , "quantity" , "anaesthetists?" .)