ferociousness vs cruelty

ferociousness and cruelty both are nouns.

Word	Noun	Adjective	Verb	Adverb
ferociousness	Yes	No	No	No
cruelty	Yes	No	No	No

As nouns, cruelty is a hypernym of ferociousness; that is, cruelty is a word with a broader meaning than ferociousness:

Other hypernyms of ferociousness include cruelness, harshness.

ferociousness (noun)	cruelty (noun)
the trait of extreme cruelty	a cruel act; a deliberate infliction of pain and suffering
	the quality of being cruel and causing tension or annoyance
	feelings of extreme heartlessness