- odd or irrational; crazy: They had some wacky plan for selling more books.
Origin of wacky
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
- slang eccentric, erratic, or unpredictable
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)
Word Origin and History for wackiness
"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