'ataraxia' originates from Ancient Greek, specifically the word 'ἀταραξία' (ataraxia), where the prefix 'a-' meant 'not' and 'taraxia' (from 'tarassein'/'tarachē') meant 'disturbance' or 'confusion'.

'ataraxia' passed into Medieval/Modern Latin as 'ataraxia' and entered English usage via philosophical and medical writings, keeping the form 'ataraxia' with the plural 'ataraxias' in modern English.

Initially, it meant 'absence of disturbance; calmness' in Greek, and over time it has retained this core sense as 'serene calmness or imperturbability' in modern usage.