1) Absurd 2) Asinine 3) Daft 4) Foolish 5) Idiotic 6) Inane 7) Insane 8) Loony 9) Mad 10) Nutty 11) Outrageous 12) Stupid 13) Tomfool 1) Absurd 2) Fatuitous 3) Foolish 4) Half-baked 5) Impractical 6) Insane 7) Like some schemes 8) Loopy 9) Organically foolish 10) Ridiculous 11) Silly 12) Unwise 13) Very foolish 
Hare'brained` (hâr'brānd`) adjective Wild; giddy; volatile; heedless. 'A mad hare-brained fellow.' North (Plutarch). [ Written also hairbrained .]
[adj] - very foolish
insane adjective very foolish; `harebrained ideas`; `took insane risks behind the wheel`; `a completely mad scheme to build a bridge between two mountains`