mistress vs schoolteacher

mistress and schoolteacher both are nouns.

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

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

Other hypernyms of mistress include school teacher, adult female, woman.

mistress (noun)	schoolteacher (noun)
a woman master who directs the work of others	a teacher in a school below the college level
an adulterous woman; a woman who has an ongoing extramarital sexual relationship with a man
a woman schoolteacher (especially one regarded as strict)