A shameless falsehood. For example, Bill could tell a barefaced lie with a straight face. The adjective barefaced means "beardless," and one theory is that in the 1500s this condition was considered brazen in all but the youngest males. By the late 1600s barefaced also meant "brazen" or "bold," the meaning alluded to in this phrase.
Dictionary.com presents 366 FAQs, incorporating some of the frequently asked questions from the past with newer queries.