ferociousness vs cruelness

ferociousness and cruelness both are nouns.

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

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

Other hypernyms of ferociousness include cruelty, harshness.

ferociousness (noun)	cruelness (noun)
the trait of extreme cruelty	the quality of being cruel and causing tension or annoyance