'kefir' originates from Russian, specifically the word 'кефир', where 'кеф' meant 'foam' or 'froth'.

'кефир' changed from the Turkish word 'kef', which referred to the frothy nature of the drink, and eventually became the modern English word 'kefir'.

Initially, it meant 'a frothy or foamy drink', but over time it evolved into its current meaning of 'a fermented milk drink'.