hare-brained (adj.)youdaoicibaDictYouDict[hare-brained 词源字典]
also harebrained, 1540s, from hare-brain "giddy or reckless person" (1540s), probably from hare (n.), on notion of "flighty, skittish."[hare-brained etymology, hare-brained origin, 英语词源]