He shook his head disappointedly and put the report card back on the table.

disappointedly 是副词，由形容词 disappointed（感到失望的）加上副词后缀 -ly 构成。disappointed 来自动词 disappoint（使失望），由前缀 dis-（表示否定）和 appoint（任命、指定）组成，字面意思是"使未能如愿"。 disappointedly 表示"以失望的方式"，描述摇头时的情绪状态。