The word "同流合污" is formed by combining the characters 同 (together), 流 (flow), 合 (join), and 污 (filth) into two paired elements: "同流" literally means to flow together or share the same current, and "合污" means to join in filth; these are concatenated to create a metaphorical phrase where the literal image of merging with a dirty stream figuratively represents aligning with or participating in immoral or corrupt activities.