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

'Ἀλάστωρ' transformed into the Latin word 'alastor', 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 'avenging spirit'.