Transaction includes book about molars (6)
I believe the answer is:
dental
'transaction includes book about molars' is the definition.
I can't judge whether this definition defines the answer.
'transaction includes book' is the wordplay.
'transaction' becomes 'deal' (a deal is a transaction or exchange).
'includes' is an insertion indicator.
'book' becomes 'NT' (New Testament).
'deal' placed around 'nt' is 'DENTAL'.
Can you help me to learn more?
(Other definitions for dental that I've seen before include "sort of surgeon" , "surgery" , "Pertaining to teeth" , "Relating to teeth" , "Concerning teeth" .)