cruelness vs cruelty

cruelness and cruelty both are nouns.

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

As nouns, cruelness and cruelty are synonyms defined as:

cruelness and cruelty: the quality of being cruel and causing tension or annoyance

Other synonyms of cruelness include harshness.

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