/ Dictionary / Index W whacko: Meaning and Definition of Find definitions for: whack•o Pronunciation: (hwak'ō, wak'ō), [key] — n., pl. adj. whack•os, —n. wacko. —adj. wacky. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: whacko (Thesaurus) whacking whacky Related Content Daily Word Quiz: sinister Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language