calcedony vs onyx

calcedony and onyx both are nouns.

Word	Noun	Adjective	Verb	Adverb
calcedony	Yes	No	No	No
onyx	Yes	No	No	No

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

calcedony: a milky or greyish translucent to transparent quartz
onyx: a chalcedony with alternating black and white bands; used in making cameos

Other hyponyms of calcedony include agate, bloodstone, heliotrope, carnelian, cornelian, chrysoprase, plasma, sard, sardine, sardius.

calcedony (noun)	onyx (noun)
a milky or greyish translucent to transparent quartz	a chalcedony with alternating black and white bands; used in making cameos