Definition of wackadoo in US English:

wackadoo

(also whackadoo)

noun

US
informal
  • An eccentric or fanatical person.

    ‘he seems like a good guy even if he is a wackadoo’
    • ‘Ellen is a hysterically needy wackadoo whom Jason takes up with when Stacy walks out on him.’
    • ‘Anyone who thinks an ugly planet is a healthy planet is a wackadoo.’
    • ‘Elevating these wackadoos to even the most carefully vetted legitimacy lowers a writer to an idiot.’
    • ‘I've just happened to come across quite a few wackadoos in my time.’
    • ‘His fanbase shifted from horny teens and MTV devotees to hardcore wackadoos.’
    • ‘Will we see fewer interviews with wackadoos in the street and just general mayhem?’
    • ‘Please do not let one wackadoo ruin it for the rest of us.’
    • ‘Some of the whackadoos are partially correct.’
    • ‘It annoys the hell out of me when wackadoos like this reproduce!’
    oddity, odd fellow, unorthodox person, character, individualist, individual, free spirit, misfit
    zealot, extremist, militant, dogmatist, devotee, sectarian, bigot, chauvinist, partisan, radical, diehard, ultra, activist, apologist, adherent
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adjective

US
informal
  • Eccentric or fanatical.

    ‘out of the blue, he would do something completely wackadoo’
    • ‘The five minutes Lloyd spends reprising his wackadoo role as the piranha-infatuated biologist are entertaining enough.’
    • ‘It takes a little time to get over the wackadoo premise and for the show to really warm up.’
    • ‘The worst part of it is the crazy, whackadoo headdress she makes her model wear.’
    • ‘In hindsight, though, they do seem like pretty whackadoo ideas.’
    • ‘I think he and Jill make a lovely whackadoo couple.’
    • ‘Luckily, they found an ad campaign that adequately suits his whackadoo personality.’
    • ‘So there is your factual evidence, but I'm sure you'll give some wackadoo response to justify your unique and frankly odd position!’
    • ‘He hosts a whackadoo talk show, complete with offbeat musical happenings.’
    • ‘Sure, the movie has some wackadoo charm but the modern remakes, recently released on Blu-ray and DVD, are just a waste of time.’
    • ‘The wackadoo radio host and conspiracy-monger is posting about this on Facebook and Twitter.’
    unconventional, uncommon, abnormal, irregular, aberrant, anomalous, odd, queer, strange, peculiar, weird, bizarre, off-centre, outlandish, freakish, extraordinary
    enthusiastic, eager, keen, fervent, ardent, fervid, passionate, devoted, dedicated
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Origin

1950s: probably from wack or wacky.

Pronunciation

wackadoo

/ˈwakəˌdo͞o/