'hasn't' originates from the contraction of 'has' and 'not', where 'has' is derived from Old English 'hæfð', meaning 'to have'.

'has' changed from the Old English word 'hæfð' and eventually became the modern English word 'has'.

Initially, 'has' meant 'to possess or own', but over time it evolved into its current auxiliary verb usage in contractions like 'hasn't'.