The Collaborative International Dictionary of English v.0.48:
Hairbrained \Hair"brained`\ (h[^a]r"br[=a]nd`), a. See Harebrained. HairbreadthThe Collaborative International Dictionary of English v.0.48:
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]