ADJ-GRADED [usually ADJ n](计划、理论)愚蠢的,不切实际的 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. (计划、理论)愚蠢的,不切实际的 [disapproval]
This isn't the first hare-brained scheme he's had.