will-o'-the-wisp (n.)youdaoicibaDictYouDict[will-o'-the-wisp 词源字典]
1660s, earlier Will with the wisp (c. 1600), from the masc. proper name Will + wisp "bundle of hay or straw used as a torch." Compare Jack o'lantern.[will-o'-the-wisp etymology, will-o'-the-wisp origin, 英语词源]