The most common and most likely answer to this crossword clue is the 3 plus 9 letter word OLD TESTAMENT
I've seen this crossword clue in The Guardian
O
L
D
T
E
S
T
A
M
E
N
T
More clues leading to the result OLD TESTAMENT
- Head of Oxford keen to accept daughter to examine some books
- Job found here, modest talent developed
- Modest talent written about in books
- Numbers in this sub-zero temperature expanded?
- OT sprayed Dettol over part of fower
- International match depicted in medal — not unusual in ancient books
- Writings that could become modest talent
Buddy explains!
The straight part
We know that "Numbers in this" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case numbers in this = old testament.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.