The negotiation began with seemingly friendly exchanges, which later turned into heated arguments.

seemingly 是副词，由形容词 seeming（表面上的）加上副词后缀 -ly 构成。seem 是动词，意思是"看起来、似乎"，seeming 表示"表面上的、看似真实的"。seemingly 用来描述事物表面上看起来的样子，暗示实际情况可能并非如此。