fierceness vs furiousness

fierceness and furiousness both are nouns.

Word	Noun	Adjective	Verb	Adverb
fierceness	Yes	No	No	No
furiousness	Yes	No	No	No

As nouns, fierceness and furiousness are synonyms defined as:

Other synonyms of fierceness include ferocity, fury, vehemence, violence, wildness.

fierceness (noun)	furiousness (noun)
the property of being wild or turbulent	the property of being wild or turbulent