peen (n.)youdaoicibaDictYouDict[peen 词源字典]
1680s, "sharp or thin end of a hammer head, opposite the face," probably from a Scandinavian source (compare Norwegian dialectal penn "peen," Old Swedish pæna "beat iron thin with a hammer"). Earlier as a verb, "to beat thin with a hammer" (1510s).[peen etymology, peen origin, 英语词源]