To overrule is to veto something or to use your authority to make a different decision than others have made or suggested.(verb)
When your boss says you can have a raise butthe president of the company steps in and says that you cannot have a raise so the raise never goes through, this is an example of when the president overrules your boss.
See overrule in Webster's New World College Dictionary
See overrule in American Heritage Dictionary 4
transitive verb o·ver·ruled, o·ver·rul·ing, o·ver·rules
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