Indefeasibility is a legal term that refers to the absolute or incontestable nature of a property right or title. There are several synonyms for this term, such as absolute, uncontestable, unquestionable, conclusive, and irrefutable. These synonyms emphasize the idea that something is not able to be disputed, challenged, or overturned. Other synonyms for indefeasibility include certain, final, settled, and firm. These terms convey the same sense of permanence and immutability as indefeasibility, and they are often used interchangeably in legal contexts. Overall, the synonyms for indefeasibility capture the idea of an unassailable and incontrovertible right or claim.