Buoyant means able to float or stay on top of water. A buoyant object bobs on the surface instead of sinking. Cork is extremely buoyant, which is why fishermen use it for floats and why old-fashioned life jackets were stuffed with cork. A beach ball is buoyant because it's filled with air. Ice is buoyant too, which is why ice cubes float in your drink and icebergs tower above the ocean.

Scientists explain buoyancy through a principle discovered by the ancient Greek mathematician Archimedes: an object floats when it weighs less than the water it pushes aside. That's why huge steel ships can float even though steel itself would sink: the ship's hollow hull is filled with air, making the whole vessel light enough to stay afloat.

The word also describes a cheerful, energetic mood. Someone with a buoyant personality seems to bounce through life with optimism and enthusiasm. After hearing good news, you might feel buoyant, as if you're floating on air. A buoyant economy is one that's growing and thriving. In this sense, buoyant suggests the same upward, floating quality, just applied to feelings or situations rather than physical objects.