'allantois' originates from Greek, specifically the word 'allantoeidēs,' where 'allanto-' meant 'sausage' and '-eidēs' meant 'form or shape.'

'allantoeidēs' transformed into the Latin word 'allantois,' and eventually became the modern English word 'allantois.'

Initially, it meant 'sausage-shaped,' but over time it evolved into its current meaning of 'a membranous sac in embryos.'