n. A person who acts as if he knows all about everything; someone who thinks no one can tell him anything new. After George was elected as class president, he wouldn't take suggestions from anyone; he became a know-it-all. Also used like an adjective. The other students didn't like George's know-it-all attitude.
KNOW-IT-ALL
Meaning of KNOW-IT-ALL in English
American idioms English vocabulary. Английский словарь американских идиом. 2012