WACKO Meaning of WACKO in English I. adjectivealso whacko ˈwa-(ˌ)kōEtymology: by alteration Date: 1975: wacky II. nounalso whackoDate: 1976: a person who is wacky ; also : psycho Merriam-Webster's Collegiate English vocabulary. Энциклопедический словарь английского языка Merriam Webster. 2003