The crossword solution for the term INVALIDATE, AS A MARRIAGE is ANNUL. 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 is a declaration that the marriage was never valid in the first place. Annulment is usually granted when there is evidence that the marriage was not legally valid, such as when one of the spouses was already married or when one of the spouses was underage at the time of the marriage.