Pronunciation: (u-nul'), [key]
—v.t., -nulled, -nul•ling.
1. (esp. of laws or other established rules, usages, etc.) to make void or null; abolish; cancel; invalidate: to annul a marriage.
2. to reduce to nothing; obliterate.
3. to cancel (a regularly scheduled train, plane, social event, etc.) for one day or one time only.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.