sullenness vs moodiness

sullenness and moodiness both are nouns.

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

As nouns, moodiness is a hypernym of sullenness; that is, moodiness is a word with a broader meaning than sullenness:

sullenness (noun)	moodiness (noun)
a sullen moody resentful disposition	having temperamental and changeable moods
a gloomy ill-tempered feeling	a sullen gloomy feeling