Shameless, impudent. This simile probably has the same source as brazen, which can mean either “made of brass” or “shameless,” “too bold.” The latter is older, dating at least from Shakespeare’s time (“What a brazen-faced varlet art thou!” King Lear, 2.2). The present cliché dates from the late seventeenth or early eighteenth century, although brass alone in the sense of “shameless” is older (sixteenth century). “Can any face of brass hold longer out?” wrote Shakespeare in Love’s Labour’s Lost (5.2), and Thomas Fuller (The Profane State, 1642) wrote still more explicitly, “His face is of brasse, which may be said either ever or never to blush.”