'backbiter' originates from Modern English as a compound of 'back' + 'bite' + the agent suffix '-er', where 'back' originally meant 'the rear or behind' and 'bite' meant 'to bite'.

'backbiter' developed from Middle English forms such as 'bakbiten' (a compound of 'bak' + 'biten'), which in turn trace to Old English/Germanic elements: Old English 'bæc' (back) and 'bītan' (to bite).

Initially the elements referred to the literal idea of biting at the back; over time the compound evolved metaphorically to mean 'to attack someone's reputation secretly' and today denotes someone who speaks ill of others behind their back.