Late 19th century. From post-classical Latin achromos or its etymon ancient Greek ἄχρωμος colourless + -ous. Compare earlier achromatous, and also achromatistous and achroous.
Definition of achromous in US English:
achromous
adjectiveeɪˈkrəʊməs
rare
Uncoloured; colourless.
Origin
Late 19th century. From post-classical Latin achromos or its etymon ancient Greek ἄχρωμος colourless + -ous. Compare earlier achromatous, and also achromatistous and achroous.