'undying' originates from Old English, specifically the prefix 'un-' meaning 'not' and the word 'dying' from 'die', where 'die' meant 'to cease living'.

'undying' changed from the Old English word 'undie' and eventually became the modern English word 'undying'.

Initially, it meant 'not dying or ceasing to live', but over time it evolved into its current meaning of 'everlasting or eternal'.