What is the legal term for a person who is not of sound mind?

The term "non compos mentis" is the correct legal terminology used to describe a person who is not of sound mind. This Latin phrase translates to "not of sound mind," and it is often applied in legal contexts to indicate an individual who lacks the ability to make informed decisions due to mental impairments or disorders. In various legal scenarios, such as when determining a person’s capacity to enter contracts or make medical decisions, establishing that someone is non compos mentis can have significant implications for their rights and responsibilities.

While other terms like "incapacitated," "competent," and "legally unfit" relate to mental capacity or legal standing, they do not specifically convey the precise lack of soundness of mind that "non compos mentis" denotes. "Incapacitated" refers generally to a person's inability to carry out certain activities, which may not necessarily imply a complete lack of mental soundness. "Competent" signifies the opposite, indicating that a person has the mental capacity to make decisions. "Legally unfit" is a more vague term that could potentially encompass a range of circumstances but does not specifically refer to the condition of being unable to think rationally or comprehensively.