psycho

¹ American  

[sahy-koh] / ˈsaɪ koʊ /

noun

plural

psychos

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-.

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 ( 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

King’s captive-author nightmare gets classed up by two knockout performances calibrated in perfect harmony: Kathy Bates’ psycho fan, a turn that earned her an Oscar, and James Caan as the bedbound writer.

From Los Angeles Times • Dec. 15, 2025

The film is part psycho kidnapping horror, part shark thriller and part tribute to Madonna’s “Ray of Light.”

From Salon • Jun. 8, 2025

It’s not a psycho performance, but it is a singular one.

From New York Times • Apr. 26, 2023

I smacked him on the arm so he’d look at my impersonation of the psycho look on his face.

From "We Were Here" by Matt De La Peña