'overreaction' originates from the prefix 'over-' meaning 'excessive' and the word 'reaction' from Latin 'reactio', where 're-' meant 'again' and 'actio' meant 'action'.

'reactio' transformed into the French word 'réaction', and eventually became the modern English word 'reaction', with 'over-' added to form 'overreaction'.

Initially, it meant 'an action in response to something', but over time it evolved into its current meaning of 'an excessive response'.