appendicular skeleton vs pelvic arch

appendicular skeleton and pelvic arch both are nouns.

Word	Noun	Adjective	Verb	Adverb
appendicular skeleton	Yes	No	No	No
pelvic arch	Yes	No	No	No

appendicular skeleton (noun)	pelvic arch (noun)
the part of the skeleton that includes the pectoral girdle and the pelvic girdle and the upper and lower limbs	the structure of the vertebrate skeleton supporting the lower limbs in humans and the hind limbs or corresponding parts in other vertebrates