'accustomed' originates from Middle English, specifically the word 'accustumed,' where 'ac-' meant 'to' and 'custom' meant 'habit or practice.'

'accustumed' changed from the Old French word 'acostumer' and eventually became the modern English word 'accustomed'.

Initially, it meant 'to make familiar through use or habit,' and this meaning has largely remained the same in modern usage.