'customarily' originates from the Latin word 'consuetudinarius,' where 'consuetudo' meant 'custom or habit.'

'Consuetudinarius' transformed into the Old French word 'costumier,' and eventually became the modern English word 'customary,' from which 'customarily' is derived.

Initially, it meant 'according to custom or habit,' and this meaning has largely remained the same in modern usage.