appendicular skeleton vs endoskeleton

appendicular skeleton and endoskeleton both are nouns.

Word	Noun	Adjective	Verb	Adverb
appendicular skeleton	Yes	No	No	No
endoskeleton	Yes	No	No	No

appendicular skeleton (noun)	endoskeleton (noun)
the part of the skeleton that includes the pectoral girdle and the pelvic girdle and the upper and lower limbs	the internal skeleton; bony and cartilaginous structure (especially of vertebrates)