'astomatous' originates from Neo-Latin/Modern Latin, formed from the privative prefix 'a-' (from Greek) + Greek 'stoma' meaning 'mouth, opening', with the English adjective-forming suffix '-ous'.

'astomatous' was formed from Neo-Latin/Modern Latin elements (e.g. 'astomatus' or similar coinages used in scientific Latin) and was adopted into English as the adjective 'astomatous' in botanical and anatomical contexts.

Initially it meant 'without a mouth or opening' in a general sense; over time it has come to be used especially in botany to mean 'lacking stomata'.