'allantois-bearing' originates from Modern English compounding of the noun 'allantois' and the verb/participle 'bearing', where 'allantois' referred to a specific extra-embryonic membrane and 'bearing' meant 'carrying' or 'possessing'.

'allantois' comes from New Latin 'allantois', ultimately from Ancient Greek (e.g. ἀλλαντοειδής / allantoeidēs) meaning 'sausage-shaped'; the term was adopted in anatomical and embryological Latin and then into English as 'allantois', later forming the compound adjective 'allantois-bearing'.

Initially the Greek root described a 'sausage-shaped' form, but over time 'allantois' came to denote a specific embryonic membrane; 'allantois-bearing' thus evolved to mean 'having that membrane'.