Serious and unrelenting in attitude or appearance.

गंभीर और कठोर

English Usage: She gave him a stern look when he arrived late.

Hindi Usage: जब वह देर से आया तो उसने उसे गंभीर नज़र से देखा।

A strict and serious person, often seen as harsh or forbidding.

कठोर व्यक्ति

English Usage: The teacher had a stern demeanor that kept the students in line.

Hindi Usage: शिक्षक का व्यक्तित्व कठोर था जो छात्रों को अनुशासित रखता था।

In a serious or strict manner.

गंभीरता से

English Usage: He spoke sternly to warn them about the consequences.

Hindi Usage: उसने गंभीरता से उन्हें परिणामों के बारे में चेतावनी दी।