embitterment vs unhappiness

embitterment and unhappiness both are nouns.

Word	Noun	Adjective	Verb	Adverb
embitterment	Yes	No	No	No
unhappiness	Yes	No	No	No

As nouns, unhappiness is a hypernym of embitterment; that is, unhappiness is a word with a broader meaning than embitterment:

embitterment: the state of being embittered
unhappiness: state characterized by emotions ranging from mild discontentment to deep grief

embitterment (noun)	unhappiness (noun)
the state of being embittered	emotions experienced when not in a state of well-being
	state characterized by emotions ranging from mild discontentment to deep grief