Book border held in both hands (6)
I believe the answer is:
ledger
'book' is the definition.
(synonyms)
'border held in both hands' is the wordplay.
'border' becomes 'edge' (synonyms).
'held in' indicates putting letters inside.
'both hands' becomes 'lr' (abbreviations for left and right).
'edge' going into 'lr' is 'LEDGER'.
(Other definitions for ledger that I've seen before include "In which accounts are entered" , "Account book" , "record-holder" , "Accounting journal" , "Old accounts book" .)