The oppressed workers united to demand better working conditions.

oppressed 是动词 oppress 的过去分词形式，在句中作形容词使用。oppress 由前缀 op-（表示"对抗"）和词根 press（压）组成，意思是"压迫、压制"。oppressed 表示"被压迫的、受压迫的"。