'backslide' originates from English, specifically the elements 'back' + 'slide', where 'back' meant 'backward' and 'slide' meant 'to slip or move smoothly.'

'backslide' developed from earlier phrases like 'to slide back' and by Early Modern English became the compound 'backslide'; the modern derivative 'backliding' formed by adding the -ing suffix.

Initially it referred more literally to 'slipping or moving backward'; over time it came to mean 'reverting to a previous (often worse) behavior or state,' especially in moral or religious contexts.