And so, putting her back on the shelf, I turned to the other great lady, The Duchess whom Lamb loved, hare-brained, fantastical Margaret of Newcastle, her elder, but her contemporary.
disapproval You use hare-brained to describe a scheme or theory which you consider to be very foolish and which you think is unlikely to be successful or true. This isn't the first hare-brained scheme he's had. = crackpot. a hare-brained plan or idea is very silly or unlikely to succeed