'astomous' originates from Ancient Greek, specifically the word 'astōmos' (ἀστόμος), where the prefix 'a-' meant 'without' and 'stoma' meant 'mouth' or 'opening'.

'astomous' entered English scientific usage via New Latin/Modern scientific coinage based on Greek roots (compare New Latin forms such as 'astomatus') and has been used in zoological and botanical descriptions since the 19th century.

Initially it meant 'without a mouth' in the literal Greek sense, and over time it has been maintained in technical usage to mean either 'without a mouth' (zoology) or 'without stomata' (botany).