Show bank book (8)
I believe the answer is:
proverbs
'book' is the definition.
(I've seen this before)
'show bank' is the wordplay.
'show' becomes 'prove' (proving is a kind of showing).
'bank' becomes 'rbs' (I can't justify this - if you can you should believe this answer much more).
'prove'+'rbs'='PROVERBS'
Can you help me to learn more?
(Other definitions for proverbs that I've seen before include "Adages, saws" , "Gnomes" , "Book of the Bible" , "More than one saw" , "Truthful expressions" .)