What is the origin of ataraxia?

Ataraxia “freedom from anxiety” is a borrowing from the Ancient Greek noun ataraxía “impassiveness, calmness,” which is based on the adjective ataráktos “unmoved.” Ataráktos, in turn, is a derivative of the verb tarássein (stem tarak-) “to disturb,” plus the prefix a- “not, without.” One major proponent of ataraxia is the philosopher Epicurus, the inspiration for the recent Word of the Day epicurean. When we discuss the “Ancient Greek” language, we usually mean the Attic dialect of Ancient Greek spoken in the 5th and 4th centuries BC. However, where other Ancient Greek dialects have -ss-, Attic has -tt-, and for these words, Ancient Greek dictionaries opt for the more generic tarássein over the Attic taráttein. This means that, if your name is Melissa, from the Ancient Greek word for “honeybee,” you would be known throughout most of Ancient Greece as Mélissa but in Attica as Mélitta. Ataraxia was first recorded in English in the first decade of the 17th century.