zygomatic arch vs os

zygomatic arch and os both are nouns.

Word	Noun	Adjective	Verb	Adverb
zygomatic arch	Yes	No	No	No
os	Yes	No	No	No

As nouns, os is a hypernym of zygomatic arch; that is, os is a word with a broader meaning than zygomatic arch:

zygomatic arch: the slender arch formed by the temporal process of the cheekbone that bridges to the zygomatic process of the temporal bone
os: rigid connective tissue that makes up the skeleton of vertebrates

Other hypernyms of zygomatic arch include bone.

zygomatic arch (noun)	os (noun)
the slender arch formed by the temporal process of the cheekbone that bridges to the zygomatic process of the temporal bone	rigid connective tissue that makes up the skeleton of vertebrates
	a mouth or mouthlike opening