He honked his horn furiously when another car cut him off.

furiously 是形容词 furious 的副词形式，furious 来自名词 fury（愤怒），意思是"狂怒的、暴怒的"。furiously 表示"愤怒地、猛烈地"，形容动作带有强烈的愤怒情绪。