Account book on the shelf (6)
I believe the answer is:
ledger
'account book' is the definition.
(I know that account book can be written as ledger)
'the shelf' is the wordplay.
I cannot quite see how this works, but
'shelf' could be 'ledge' (synonyms) and 'ledge' is found within the answer.
A single letter 'r' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
'on' is the link.
Can you help me to learn more?
(Other definitions for ledger that I've seen before include "In which accounts are entered" , "Accounting journal" , "Old accounts book" , "Book for keeping financial accounts" , "Old-fashioned heavy accounts book" .)