The term INVALIDATE A MARRIAGE can be summarized by the word ANNUL, which is a five-letter word. Annulment is a legal process that declares a marriage null and void, as if it never existed. It is different from divorce in that it does not require a period of separation or a court hearing. Annulment is typically used when a marriage is found to be invalid due to certain circumstances, such as fraud, bigamy, or lack of consent.