'backfiller' originates from English, specifically formed from 'back' + 'fill' + the agentive suffix '-er', where 'back' originally meant 'the rear' and 'fill' meant 'to make full or to fill in'.

'back' derives from Old English 'bæc' meaning 'the rear', and 'fill' derives from Old English 'fyllan' meaning 'to fill'; these elements combined in Middle and Modern English to form the verb/noun 'backfill', and the agent noun 'backfiller' developed from that combination.

Initially it referred literally to the action or material used to fill in behind something (to 'back-fill'); over time it broadened to include a person or device that performs that filling and, by extension, someone who temporarily fills a job or role.