'dietarily' originates from 'dietary', which comes from 'diet', ultimately from the Greek word 'diaita', where 'diaita' meant 'way of life' or 'regimen'.

'diet' changed from the Old French word 'diète', from Latin 'diaeta', and eventually became the modern English word 'diet'. 'Dietary' was formed from 'diet' with the suffix '-ary', and 'dietarily' was formed by adding '-ly'.

Initially, 'diet' meant 'way of life' or 'regimen', but over time it evolved into its current meaning of 'the kinds of food that a person, animal, or community habitually eats', and 'dietarily' now means 'in a manner relating to diet'.