châtier

A formal, somewhat literary verb meaning to punish or chastise, often for moral or educational correction rather than simple retaliation. It also has a specific literary sense: châtier son style/langage means to refine or polish one's language to a very correct, elevated register.

• Les parents d'autrefois châtiaient sévèrement leurs enfants. — Parents in the past punished their children severely.
• L'auteur châtie son style dans ce roman tardif. — The author refines his style in this later novel.
• Il fut châtié pour sa désobéissance. — He was punished for his disobedience.

Châtier is more formal and literary than punir — reach for punir in ordinary conversation about disciplining a child; châtier belongs more to formal, moral, or literary registers (or its 'refine language' sense).

• expression "Qui aime bien châtie bien" — A well-known French proverb, a literal translation of the medieval Latin adage "Qui bene amat, bene castigat," meaning real love sometimes requires discipline or correction.