'nonallantoic' originates from the Modern English negative prefix 'non-' (meaning 'not') combined with 'allantoic', which derives from Greek 'allantois' meaning 'sausage-shaped' (used in anatomy to describe the allantois).

'allantois' entered scientific/medical Latin from Greek 'allantois'; English formed the adjective 'allantoic' from this, and later the negative prefix 'non-' was attached in English to create 'nonallantoic'.

The components originally referred specifically to the allantois (a sausage-shaped embryonic structure); 'nonallantoic' developed as a straightforward negative formation meaning 'not pertaining to the allantois'.