In a manner that is light, cheerful, and optimistic, or in a way that floats or rises easily.
From buoyant + -ly (adverb suffix). Buoyant derives from buoy, with -ant, and originally meant 'able to float'; it later acquired the figurative sense of 'cheerful' or 'optimistic,' and the adverb form followed.
It's fascinating that the same word describes both floating objects and floating spirits—the metaphor of rising upward connected physical buoyancy with emotional optimism, making 'buoyantly' describe everything from bouncing balls to bouncing personalities.
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