Warn off is a phrase that means to advise or caution someone to stay away from someone or something because of danger or a potential threat. There are many synonyms that can be used in place of warn off, such as discourage, dissuade, caution, advise against, forbid, prohibit, deter, or ward off. These words can be used interchangeably depending on the context and severity of the situation. For instance, when one is warning someone against getting involved in an illegal activity, it is best to use the word prohibit or dissuade. Meanwhile, the word ward off can be used when there is a threat of danger or harm.