'backlash' originates from English, specifically the compound of 'back' and 'lash', where 'back' meant 'the rear' or 'behind' and 'lash' meant 'a strike' or 'sudden movement'.

'backlash' first appeared in technical/mechanical usage in the 19th century to describe a 'recoil' or 'play' between mechanical parts; later the term was extended metaphorically to describe a 'strong adverse reaction' in social and political contexts.

Initially, it meant 'mechanical recoil or play', but over time it evolved into its common modern sense of 'a sudden, adverse reaction (especially public or political)'.