very foolish“harebrained ideas”“took insane risks behind the wheel”“a completely mad scheme to build a bridge between two mountains”Synonyms: insanemad
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Webster's Dictionary (GCIDE)
Harebrained \Hare"brained`\ (h[^a]r"br[=a]nd`), a. Wild; giddy; volatile; heedless. "A mad hare-brained fellow." --North (Plutarch). [Written also hairbrained.] [1913 Webster]