sullenness vs sulkiness

sullenness and sulkiness both are nouns.

Word	Noun	Adjective	Verb	Adverb
sullenness	Yes	No	No	No
sulkiness	Yes	No	No	No

As nouns, sullenness and sulkiness are synonyms defined as:

Other synonyms of sullenness include moroseness, sourness.

sullenness (noun)	sulkiness (noun)
a sullen moody resentful disposition	a sullen moody resentful disposition
a gloomy ill-tempered feeling	a feeling of sulky resentment
	a mood or display of sullen aloofness or withdrawal