When talking about legal matters, "party in interest" refers to an individual or entity who has a stake or interest in a particular matter. Some synonyms for this term include "interested party," "affected party," "concerned party," "related party," "stakeholder," "invested party," and "participant." These terms all refer to someone who has a vested interest in the outcome of a legal decision, dispute, or transaction. It's important to accurately define these terms when dealing with legal matters to ensure that everyone involved understands their role and level of interest. By using these synonyms interchangeably, legal professionals can clearly communicate a party's involvement in a particular matter.