Key Difference: The term ‘psycho’ comes from the word psychological which in turn refers to anything to do with the mind. Similarly, the term mental also refers to anything to do with the mind. However, over time both these words were absorbed into common vernacular and began to be used as slang.

Psycho and Mental are two terms that used to be related to mental health, however these days they are commonly used as slang terms to refer to people that display behaviors that are not socially accepted.

The term ‘psycho’ comes from the word psychological which in turn refers to anything to do with the mind. Similarly, the term mental also refers to anything to do with the mind. Originally, the term psychological developed as a more scientific term to professionally refer to things that would have otherwise be referred to as ‘mental’.

However, over time both these words were absorbed into common vernacular and began to be used as slang. The term ‘psycho’ is informally and incorrectly used as a slang for ‘psychopath.’ Yet it should be noted, that it not technically used only for people who have been officially diagnosed at a psychopath, instead it is used for any person who behaves out of the norm, or depicts behavior that people gauge as being psychotic, i.e. not normal, or ‘crazy.’ Hence, any person who doesn’t act as society deems they should are often labeled as psycho. A psycho is generally considered to be a crazy or mentally unstable person, but most of the time it is just a regular people displaying irregular behavior.