'alastor' originates from Greek, specifically the word 'Ἀλάστωρ', where 'ἀ-' meant 'not' and 'λάστωρ' meant 'to forget'.

'Ἀλάστωρ' was used in ancient Greek to describe spirits of vengeance and eventually became the modern English word 'alastor'.

Initially, it meant 'one who does not forget', but over time it evolved into its current meaning of 'spirit of vengeance'.