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wacky

[wak-ee]
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adjective, wack·i·er, wack·i·est. Slang.
  1. odd or irrational; crazy: They had some wacky plan for selling more books.
Also whacky.

Origin of wacky

1935–40; apparently whack (noun, as in out of whack) + -y1
Related formswack·i·ly, adverbwack·i·ness, noun
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for wackiness

wacky

adjective wackier or wackiest
  1. slang eccentric, erratic, or unpredictable
Derived Formswackily, adverbwackiness, noun

Word Origin

C19 (in dialect sense: a fool, an eccentric): from whack (hence, a whacky, a person who behaves as if he had been whacked on the head)
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for wackiness

wacky

adj.

"crazy, eccentric," 1935, variant of whacky (n.) "fool," late 1800s British slang, probably ultimately from whack "a blow, stroke," from the notion of being whacked on the head one too many times.

Online Etymology Dictionary, © 2010 Douglas Harper