hare·brained /-ˈbrend/
  (a.)輕率的,欠考慮的,粗心的
  Hare·brained a. Wild; giddy; volatile; heedless. “A mad hare-brained fellow.” --North (Plutarch). [Written also hairbrained.]
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  harebrained
       adj : very foolish; "harebrained ideas"; "took insane risks behind
             the wheel"; "a completely mad scheme to build a bridge
             between two mountains" [syn: insane, mad]