mistress vs employer

mistress and employer both are nouns.

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

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

Other hypernyms of mistress include adult female, woman.

mistress (noun)	employer (noun)
a woman master who directs the work of others	a person or firm that employs workers
an adulterous woman; a woman who has an ongoing extramarital sexual relationship with a man
a woman schoolteacher (especially one regarded as strict)