The definition of au contraire is French and means to the contrary, and it is a phrase used when someone is incorrect, wrong or says something that is the opposite of the truth.
(adjective)When a girl goes on and on about how much she doesn't like a guy and her friend believes that means she really does like him, this is an example of when someone might say au contraire.
See au contraire in Webster's New World College Dictionary
Origin: Fr