backbone vs intervertebral disk

backbone and intervertebral disk both are nouns.

Word	Noun	Adjective	Verb	Adverb
backbone	Yes	No	No	No
intervertebral disk	Yes	No	No	No

backbone (noun)	intervertebral disk (noun)
the part of a network that connects other networks together	a fibrocartilaginous disc serving as a cushion between all of the vertebrae of the spinal column (except between the first two)
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