Type of round figures describing those in the Book of Numbers (12)
I believe the answer is:
mathematical
'type of round' is the definition.
Both the answer and definition are adjectives. Maybe you can see an association between them that I can't see?
'figures describing those in the book of numbers' is the wordplay.
I cannot quite understand how this works, but
'figures' could be 'math' (I've seen this in another clue) and 'math' is present in the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for mathematical that I've seen before include "Rigorously precise" , "(Of proof) very accurate" .)