When you want to initiate legal action against someone, there are a variety of phrases you can use instead of "start a lawsuit." For example, you might "file a lawsuit," "commence legal proceedings," or "initiate litigation." Other synonyms for starting a lawsuit include "pursuing legal action," "filing a claim," or "initiating a civil case." If you're looking for an even more formal way to phrase it, you could say "bringing a cause of action," "enacting legal recourse," or "commencing a legal dispute." Whatever phrase you choose, it's important to consult with a qualified legal professional before initiating any legal proceedings.