'allantoidean' originates from the Greek word 'allantoeidēs', where 'allanto-' referred to 'sausage' due to the shape of the allantois, and '-oid' meant 'resembling'.

'allantoeidēs' transformed into the modern English word 'allantoidean' through scientific terminology.

Initially, it referred to the shape resembling a sausage, but over time it evolved into its current meaning related to the allantois in embryology.