backbone vs axial skeleton

backbone and axial skeleton both are nouns.

Word	Noun	Adjective	Verb	Adverb
backbone	Yes	No	No	No
axial skeleton	Yes	No	No	No

backbone (noun)	axial skeleton (noun)
the part of a network that connects other networks together	the part of the skeleton that includes the skull and spinal column and sternum and ribs
the part of a book's cover that encloses the inner side of the book's pages and that faces outward when the book is shelved
fortitude and determination
the series of vertebrae forming the axis of the skeleton and protecting the spinal cord
a central cohesive source of support and stability