IPA: /ˈbɔɪəntli/
KK: /ˈbujəntli/
In a way that is cheerful and full of energy; showing a lively and optimistic attitude.
She walked buoyantly into the room, spreading happiness to everyone around her.
Buoyantly is formed from "buoyant" (from the French "bouyant", meaning able to float) and the suffix "-ly" (meaning in a manner). The word "buoyantly" means in a manner that is able to float or rise, often used to describe a cheerful or lively attitude.
Think of being able to 'float' ('buoyant') and doing so 'in a manner' ('-ly') — that's why buoyantly means to act in a cheerful or lively way.