This word can echo ‘ledger’, and refer to a large copy of a book permanently placed somewhere, or a large copy of a Breviary, or some kind of transaction record. Other meanings include: a horizontal scaffolding plank running parallel to the building; a wooden rod used to hold down thatch; a slab of stone over a grave; a dialect word for a nether millstone.
In George Herbert’s poem ‘The Holy Scriptures’, it means ambassador or permanent representative:
‘Who can endear
Thy praise too much? thou are heav’ns lidger here,
Working against the states of death and hell.’
Source: George Herbert (1593-1633), quoted in John Drury, Music at Midnight: The Life and Poetry of George Herbert (London: Penguin Books, 2014), p. 9