A solemn promise is a serious commitment made by one person to another. OATH, TROTH, VOW, PLEDGE, IDO, WORD, WORDOFHONOR, INSTALLATION, and WORDOFHONOUR are all terms used to describe a solemn promise. An OATH is a formal declaration of loyalty or promise to fulfill an obligation. TROTH is a PLEDGE of faithfulness or loyalty. A VOW is a solemn promise or an act of dedication. A PLEDGE is a solemn promise to do something. IDO is an acronym for 'I do' which is often used in marriage ceremonies. A WORD is a promise or assurance given by one person to another. WORD of honor is a promise to tell the truth or to keep a promise. INSTALLATION is a formal ceremony in which someone is inducted into an office or position. WORD of honour is a promise to be honest or to keep a promise.