achromatism vs achromia

achromatism and achromia both are nouns.

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

As nouns, achromia is a hyponym of achromatism; that is, achromia is a word with a more specific, narrower meaning than achromatism:

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

Other hyponyms of achromatism include fadedness.

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