fortitude vs backbone

fortitude and backbone both are nouns.

Word	Noun	Adjective	Verb	Adverb
fortitude	Yes	No	No	No
backbone	Yes	No	No	No

As nouns, backbone is a hyponym of fortitude; that is, backbone is a word with a more specific, narrower meaning than fortitude:

fortitude: strength of mind that enables one to endure adversity with courage
backbone: fortitude and determination

Other hyponyms of fortitude include grit, gumption, guts, moxie, sand.

fortitude (noun)	backbone (noun)
strength of mind that enables one to endure adversity with courage	the part of a network that connects other networks together
	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