'ataraxic' originates from Greek, specifically the word 'ataraxia' (ἀταραξία), where the prefix 'a-' meant 'not' and 'tarache'/'tarax' meant 'disturbance' or 'confusion'.

'ataraxia' (Greek) passed into Latin and later into English as 'ataraxia' (a noun meaning 'freedom from disturbance'); the adjective 'ataraxic' was formed from that noun in English to describe a quality of being undisturbed.

Initially it referred to the state of 'freedom from disturbance' ('ataraxia'); over time an adjectival form 'ataraxic' came to mean 'calm, untroubled' when describing people or things.