The villagers were opposed to building a chemical plant in this area.

opposed 是动词 oppose 的过去分词形式，oppose 由前缀 op-（表示"对抗、反对"）和词根 pose（放置）组成，字面意思是"放在对立面"，即"反对、对抗"的意思。在这里 opposed 表示"持反对态度"的状态。