From Longman Dictionary of Contemporary Englishknow-it-allˈknow-it-all noun [countable] especially American English informal INTELLIGENTsomeone who behaves as if they know everything – used to show disapproval SYN know-all British English
Examples from the Corpus
know-it-all• OK, if you're such a know-it-all, you try and do it, then.• a twelve-year-old know-it-all 