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• psycho
  psycho

  noun

  a psychopathic or psychotic person.
• psycho-
  psycho-

  a combining form representing psyche (psychological ) and psychological (psychoanalysis ) in compound words.

psycho

¹ American  

[sahy-koh] / ˈsaɪ koʊ /

noun

psychos plural

1. a psychopathic or psychotic person.

2. a crazy or mentally unstable person.

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adjective

1. psychopathic or psychotic.

2. crazy; mentally unstable.

psycho- ² American  

1. a combining form representing psyche (psychological ) and psychological (psychoanalysis ) in compound words.

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psycho- ¹ British  

combining form

1. indicating the mind or psychological or mental processes

   psychology

   psychogenesis

   psychosomatic

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psycho ² British  

/ ˈsaɪkəʊ /

noun

1. an informal and offensive word for psychopath or psychopathic See psychopath

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Usage

What does psycho- mean? Psycho- is a combining form used like a prefix meaning either “psyche” or "psychological." Psyche denotes "the human soul, spirit, or mind," while psychological is a related yet distinct term that means "pertaining to psychology, the science of the mind or of mental states." Psycho- is often used in medical and technical terms, especially in psychology. Psycho- comes from Greek psȳchḗ, meaning “breath, spirit, soul, mind.” For more on the meaning of this word in Ancient Greek mythology, read our entry for psyche. The word psyche is at the root of the term psychedelic, which refers to the effect of hallucinogenic drugs. What are variants of psycho-?When combined with words or word elements that begin with a vowel, psycho- becomes psych-, as in psychiatry. Want to know more? Read our Words That Use article on psych-.

Other Word Forms

Noun Inflected Forms

• psychos
  plural

Etymology

Origin of psycho¹

First recorded in 1935–40; by shortening

Origin of psycho-²

< Greek, combining form of psȳchḗ breath, spirit, soul, mind; akin to psȳ́chein to blow ( see psykter)

Explanation

Psycho is a slang term for someone who is mentally unstable or afflicted with a psychosis. Your best friend risks looking like a psycho if she keeps stalking her ex-boyfriend months after their breakup. Psycho comes from the Greek word psykho, which means mental. Although the word has long been used as a prefix in words like psychologist, the pejorative term for a psychopath has only existed since the twentieth century. The word gained further notoriety after the 1960 release of Alfred Hitchcock's thriller, "Psycho." If you're always describing your boss as a psycho, you might want to think about looking for a new job.

Example Sentences

"I am just looking at her and thinking she could be sweet but a psycho, like that would be brilliant," Rachel told the other traitors.

From BBC • Jan. 6, 2026

But really, there is nothing as tedious as a psycho killer, except when it’s a song by the Talking Heads.

From Los Angeles Times • Nov. 13, 2024

“No! Bad, psycho governor! No! Sit down! Bad! Stay! Stay away from dogs!”

From New York Times • Apr. 30, 2024

“They go psycho on you, because they’re all psychopaths. They’re arrogant psychopaths with God complexes because our society has moved people to idolize doctors.”

From Seattle Times • Jul. 19, 2023

Every so often I would spring a Mrs. Dodds reference on somebody, just to see if I could trip them up, but they would stare at me like I was psycho.

From "The Lightning Thief" by Rick Riordan