Promising words are words that are used to make a promise or commitment. OATH is a four letter word that is a solemn promise or pledge, usually made in a religious context. IDO is a three letter word that is an abbreviation for 'I do, ' which is often used in marriage ceremonies. OATHS is a five letter word that is the plural form of the word OATH. IDOS is a four letter word that is the plural form of the word IDO. ISHALL is a six letter word that is an abbreviation for 'I shall, ' which is another way of expressing a promise or commitment.