bitterness vs envy

bitterness and envy both are nouns.

Word	Noun	Adjective	Verb	Adverb
bitterness	Yes	No	No	No
envy	Yes	No	Yes	No

As nouns, envy is a hyponym of bitterness; that is, envy is a word with a more specific, narrower meaning than bitterness:

bitterness: a feeling of deep and bitter anger and ill-will
envy: a feeling of grudging admiration and desire to have something that is possessed by another

Other hyponyms of bitterness include heartburning, huffishness, sulkiness, grievance, grudge, score, enviousness.

bitterness (noun)	envy (noun)
the property of having a harsh unpleasant taste	spite and resentment at seeing the success of another (personified as one of the deadly sins)
a rough and bitter manner	a feeling of grudging admiration and desire to have something that is possessed by another
the taste experience when quinine or coffee is taken into the mouth
a feeling of deep and bitter anger and ill-will

bitterness (verb)	envy (verb)
	be envious of; set one's heart on
	feel envious towards; admire enviously