'aproctous' originates from Greek, specifically the word 'aproktos', where the prefix 'a-' meant 'not' and 'proktos' meant 'anus'.

'aproctous' entered scientific English via Late Greek/Neo-Latin (Late Greek 'ἀπρόκτος' / New Latin 'aproctus') used in anatomical and zoological descriptions and eventually became the modern English adjective 'aproctous'.

Initially it meant 'not having an anus' in Greek anatomical usage, and over time it has retained that specialized meaning in modern scientific English.