Origins
The English adjective "mental," meaning "relating to the mind" or "carried out by or taking place in the mind," traces its origins to the Latin term "mentalis," which itself derives from the noun "mens, mentis," signifying "mind," "intellect," "reason," or "intention." This Latin root is well attested in classical texts and was used to denote the faculty of rational thought, distinguishing it from other concepts such as "animus," which referred to the animating spirit or soul, and "cor," the heart, often regarded as the seat of emotion.
The Latin "mens" is etymologically rooted in the Proto-Indo-European (PIE) root *men-, which carries the fundamental meaning "to think" or "to remember." This root is notably productive across a wide range of Indo-European languages, giving rise to cognates that reflect various aspects of mental activity or spirit. For instance, in Sanskrit, the word "manas" denotes the mind or the faculty of thought; in Ancient Greek, "menos" refers to spirit or force, and "mania" to madness or frenzy; in Lithuanian, "mintis" means "thought." English itself contains the word "mind," which, although not a direct descendant of Latin "mens," is related through the Germanic branch, deriving from Proto-Germanic *mundaz, which is considered a cognate rather than a borrowing.
The Latin "mens" and its derivatives, including "mentalis," were adopted into Old French, where "mental" came to mean "of the mind" or "intellectual." It is from Old French that the term entered Middle English in the late 14th century, retaining its original sense related to the intellect or mental faculties. The adoption into English was part of a broader pattern of borrowing from Latin via Old French, especially in scholarly, philosophical, and medical contexts, where Latin terminology was highly influential.
Latin Roots
the modern colloquial usage of "mental" in British English, where it can mean "foolish," "crazy," or "unstable," is a relatively recent semantic shift dating to the 20th century. This pejorative sense developed as slang and is not directly connected to the classical or medieval meanings of the term. Instead, it reflects a cultural evolution in the use of the word, where the association with the mind was extended to imply mental instability or eccentricity.
"mental" in English is a borrowing from Late Latin "mentalis," itself derived from the Latin "mens," which comes from the PIE root *men- meaning "to think." The root *men- is a well-established Indo-European root with numerous cognates across various languages, all related to thought or mind. The English word "mental" entered the language in the late 14th century through Old French, maintaining its original sense of intellectual or mind-related qualities. The contemporary slang usage of "mental" as "crazy" is a 20th-century British innovation and not part of the inherited or classical semantic field of the word.