brazen (adj.)youdaoicibaDictYouDict[brazen 词源字典]
Old English bræsen "of brass," from bræs "brass" (see brass) + -en (2). The figurative sense of "hardened in effrontery" is 1570s (in brazen-face), perhaps suggesting a face unable to show shame (see brass). To brazen it out "face impudently" is from 1550s.[brazen etymology, brazen origin, 英语词源]