maîtresse

/mɛtʁɛs/
1.
nounfeminineSing

female primary-school teacher

schoolteacher (for young children)

La maîtresse de mon fils lui a donné des devoirs pour le week-end.

My son's teacher gave him homework for the weekend.

Synonyms:institutrice, enseignante, professeure
2.
nounfeminineSing

mistress (a woman involved in an extramarital or clandestine affair)

Il a une maîtresse depuis trois ans.

He's had a mistress for three years.

Synonyms:amante