noun
overflowing with vitality; exuberant; effervescent
Describes a person, atmosphere, or group that is brimming with energy and lively spirits. Often used in written or slightly formal contexts.
彼の活気横溢したスピーチに聴衆は引き込まれた。
The audience was captivated by his speech overflowing with vitality.
新入社員たちの活気横溢な様子が職場を明るくした。
The new employees' exuberant demeanor brightened up the workplace.
A four-character compound (yojijukugo) combining 活気 (vitality) and 横溢 (overflowing). The exact origin is uncertain, but it follows a common pattern of Sino-Japanese compounds.