THESAURUS
crazy idea
absurd idea, boutade, brainstorm, capriccio, caprice, conceit, crank, craze, crotchet, fad, fancy, fantastic notion, fantasy, flimflam, fool notion, freak, freakish inspiration, harebrained idea, humor, kink, maggot, megrim, notion, passing fancy, quirk, toy, vagary, whim, whim-wham, whimsy