Definition & Meaning of "unhinged"in English

What is the origin of the term "unhinged" and how is it used?

Unhinged is an adjective that appeared in English by the 19th century to describe someone who is mentally unstable or unpredictable. The term comes from the literal image of a door coming off its hinges—something that no longer functions properly—applied metaphorically to a person whose behavior or reactions are erratic. Historically, it was derogatory, used to criticize or alarm about someone's mental state. Today it remains informal and critical, often used in casual, descriptive, or journalistic contexts rather than clinical or polite conversation.