paramour vs mistress

paramour and mistress both are nouns.

Word	Noun	Adjective	Verb	Adverb
paramour	Yes	No	No	No
mistress	Yes	No	No	No

As nouns, mistress is a hypernym of paramour; that is, mistress is a word with a broader meaning than paramour:

paramour: a woman who cohabits with an important man
mistress: an adulterous woman; a woman who has an ongoing extramarital sexual relationship with a man

Other hypernyms of paramour include fancy woman, kept woman.

paramour (noun)	mistress (noun)
a woman who cohabits with an important man	a woman master who directs the work of others
a woman's lover	an adulterous woman; a woman who has an ongoing extramarital sexual relationship with a man
	a woman schoolteacher (especially one regarded as strict)