Ethmia gigantea is a moth in the Depressariidae family. It is found in Mexico. The length of the forewings is 14.6–17.5 millimetres (0.57–0.69 in). The ground color of the forewings is darkbrownish black, nearly unicolorous on the costal half. The ground color of the hindwings is whitish, semitraslucent basally, becoming pale brownish on the apical half. Adults have been recorded in April, June and August.