His bitter resentment towards his former colleague was evident in every word he spoke.

bitter 的本义是"苦的"，形容味道，引申为"痛苦的""强烈的"，用来描述负面情绪时表示程度很深。 resentment 是名词，来自动词 resent（怨恨、愤恨），指"怨恨、不满"的情绪。 bitter resentment 表示"强烈的怨恨"，强调怨恨的程度很深。