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Definition of wacko

wacko

/ˈwæk.oʊ/
wack · o
Plural:wackos
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wacko Lexical Profile

wacko Game Scores & Validity

• noun

1

A person who is eccentric, irrational, or mentally unstable.

Example

"The late-night radio host was known for entertaining calls from every crank and wacko in the city."

Synonyms
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Antonyms
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• adjective

1

Extremely eccentric, irrational, or mentally unstable; crazy.

Example

"He came up with some pretty wacko conspiracy theories to explain the sudden power outage."

Synonyms
View all synonyms for wacko
Antonyms
View all antonyms for wacko

Word Nuance & Usage

Also spelled 'whacko'. This is an informal, derogatory slang term that should be avoided in formal contexts or when discussing genuine mental health conditions.

• Rhymes for wacko

• Nearby Words

wackadoodle
wackily
wackiness
wacko
wacky
waco
wad

Word Origin & Etymology

Coined in mid-20th-century American slang, formed by clipping the adjective 'wacky' (meaning eccentric or foolish) and adding the informal suffix '-o'.

Usage Trend

Historical frequency of usage in published text.

180019102020
Data source: Google Books Ngram Viewer

Cite this Entry

Wordmom. (2026). Definition of Wacko. In Wordmom Dictionary. Retrieved Nov 5, 2026, from https://wordmom.com/dictionary/wacko
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