'backslider' originates from English, specifically the word 'backslide' with the agentive suffix '-er', where 'back-' meant 'back' and 'slide' meant 'to slip or glide.'

'backslider' changed from Middle English verb forms such as 'baksliden' (to slip back) and later noun formations like 'bak-slider' in Early Modern English, eventually becoming the modern English word 'backslider'.

Initially, it meant 'one who slips or slides back' (a largely physical sense); over time it evolved into its current meaning of 'someone who relapses into sin or bad habits.'