Cause of action refers to the legal basis for a lawsuit or a legal claim. There are several synonyms that can be used for the term cause of action, including legal claim, grounds for action, reason for action, or basis of a lawsuit. Other synonyms for the term include allegation, complaint, or charge. In essence, the cause of action identifies the specific legal harm that the plaintiff seeks to redress by bringing a lawsuit. It is an essential element of any legal claim, as it sets out the facts that the plaintiff needs to prove in order to be successful in the lawsuit.