tarax-, tarac- (Greek > Latin: disturbed; confusion, disturbance, trouble).

ataractic [at uh RAK tik], ataraxic [at uh RAKS ik]: 1. Calm, serene.
2. In medicine, used to describe a drug or other agent that produces calm and peace of mind; a tranquilizer.

The Epicureans were especially fond of the term ataraxia which meant freedom from confusion and peace of mind. It is proposed, therefore, that drugs of this type be designated ataraxics, and that the adjectival form, ataractic, be used to describe this therapeutic property in drugs. (From the journal, Neurology, 1955). ataraxia [at uh RAK see uh], ataraxy [at uh RAK see]: 1. An idyllic state, one of complete serenity, free from anxiety, the cares of the world, or any sort of emotional upset; literally, "imperturbability".
2. Freedom from disturbance of mind or passion; stoical indifference.
3. In psychiatry, absence of anxiety or confusion; imperturbability; untroubled calmness; inner harmony; especially without depression of mental faculties or clouding of consciousness.

Etymologically from Greek ataraktos, "undisturbed, based on the negative prefix a- plus tarak, a variant stem of the verb tarassein, "to disturb, confuse".

Ataraxia was the state of calm and indifference sought as a goal by the Stoics, members of a philosophical school founded by Zeno about 300 B.C., which taught the rigid suppression of passions, self-indulgence, and unjust thoughts.

The teaching of indifference to pleasure or pain led to the definition of stoical as "impassive" with the implication of austere courage and submission without complaint to the inevitable hard knocks of life. That is considered true ataraxia.