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.