起诉 (qǐsù) is a formal legal verb meaning 'to file a lawsuit'—that is, to formally initiate legal proceedings against someone in court. The first character 起 (qǐ) means 'to begin' or 'to initiate', and the second character 诉 (sù) means 'to accuse' or 'to complain (in a legal sense)'. Together, they literally convey 'to initiate an accusation', reflecting the procedural nature of bringing a case before a judge. This word is used exclusively in legal contexts and implies official action through proper judicial channels.

起诉 is commonly used when referring to civil disputes (e.g., breach of contract), criminal complaints (e.g., by a victim or prosecutor), or administrative grievances. It requires clear evidence and adherence to procedural law. Unlike informal complaints or reporting to authorities, 起诉 specifically refers to submitting documents to a court and requesting judicial intervention. It’s not used for everyday disagreements or verbal accusations—it carries weight and consequence in Chinese legal practice.