wackadoo adjective 1noun 1forms 3 adjective1 •(slang) Crazy, wacky.See, it was these wackadoo inventions that finally got to me. That's why I asked for the trial separation. — 1992 noun1 •(slang) A crazy person; wacko.Still, she felt like a wackadoo sometimes, even if she knew she was too hard on herself; she should cut herself some slack. — 1987 formswackadoos · more wackadoo · most wackadoo