>Shameless or brazen boldness
>Insolent and shameless audacity
>Extreme rudeness without any ability to understand that your behaviour is not acceptable to other people
To the Romans, the shameless were “without forehead,” at least figuratively. Effrontery derives from Latin effrons, a word that combines the prefix ex- (meaning “out” or “without”) and “frons” (meaning “forehead” or “brow”).
>He had the effrontery to insult the guest
>He had the effrontery to address her with casual salutation with her during their formal chat
>He was not having any idea regarding her culinary skills but got the effrontery to come up with a ridiculous qualifying remark