effrontery (n.) Look up effrontery at Dictionary.com
1715, from French effronterie, from effronté "shameless," from Old French esfronte "shameless, brazen," probably from Late Latin effrontem (nominative effrons) "barefaced," from Latin ex- "out" (see ex-) + frontem (nominative frons) "brow" (see front (n.)).

Latin frontus had a sense of "ability to blush," but the literal sense of effrontery often has been taken to be "putting forth the forehead." Forehead in Johnson's Dictionary (1755) has a secondary sense of "impudence; confidence; assurance; audaciousness; audacity."