achromia vs achromatism

achromia and achromatism both are nouns.

Word	Noun	Adjective	Verb	Adverb
achromia	Yes	No	No	No
achromatism	Yes	No	No	No

As nouns, achromatism is a hypernym of achromia; that is, achromatism is a word with a broader meaning than achromia:

achromia: an absence of normal pigmentation especially in the skin (as in albinism) or in red blood cells
achromatism: the visual property of being without chromatic color

Other hypernyms of achromia include achromaticity, colorlessness, colourlessness.

achromia (noun)	achromatism (noun)
an absence of normal pigmentation especially in the skin (as in albinism) or in red blood cells	the visual property of being without chromatic color