He bowed his head and contritely admitted his mistake.

contritely 是形容词 contrite 的副词形式，由 contrite（懊悔的）加上副词后缀 -ly 构成。contrite 来自拉丁语，原意是"磨碎的"，引申为"因悔恨而内心痛苦的"。contritely 表示"懊悔地、悔恨地"，形容带着真诚悔意的态度。