Confident or certain

आश्वस्त

English Usage: She was assured of her success in the competition.

Hindi Usage: वह प्रतियोगिता में अपनी सफलता के लिए आश्वस्त थी।

To make someone feel certain or to promise

आश्वासन देना

English Usage: He assured her that everything would be fine.

Hindi Usage: उसने उसे आश्वासन दिया कि सब ठीक हो जाएगा।