noun.
The invalidation of a marriage, as for nonconsummation, effected by means of a declaration stating that the marriage was never valid.
The Century Dictionary and Cyclopedia
noun.
The act of annulling; specifically, the act of making void retrospectively as well as prospectively: as, the annulment of a marriage (as distinguished from the granting of a divorce).
the GNU version of the Collaborative International Dictionary of English
noun.
The act of annulling; abolition; invalidation.