The term 'Promise to Marry' is a phrase that has been used for centuries to signify a commitment between two people. BETROTH, with seven letters, is an old-fashioned word meaning to promise to marry someone. AFFIANCE, with eight letters, is another word for betrothal, and Plightonestroth, with fifteen letters, is an archaic term for a solemn promise to marry. All three words are related to the concept of a promise to marry and signify a commitment between two people.