Ethmia octanoma is a moth in the Depressariidae family. It is found in India, Japan, China and Taiwan. The wingspan is 20–23 mm. The forewings are overlaid with black spots on a grey background. The wing pattern consists of six black spots and an elongate group of black scales. The hindwings are bright grey, but the basal part is yellowish. The larvae feed on Ehretia resinosa and Ehretia dicksonii.