fortitude vs guts

fortitude and guts both are nouns.

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

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

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

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

fortitude (noun)	guts (noun)
strength of mind that enables one to endure adversity with courage	fortitude and determination