"Oppo" is a slang term that means opponent or enemy. Some synonyms for "oppo" are foe, rival, adversary, challenger, competition, and antagonist. Each of these words describes a person or entity that is in direct opposition to someone or something else. While "foe" and "enemy" are more commonly associated with military or violent conflicts, "rival" and "adversary" are often used in business or sports contexts. "Antagonist" is a term often used in literature or film to describe the main villain or antagonist in a story. Despite their different connotations, all of these words can be used interchangeably with "oppo" in the appropriate context.