ataraxia (n.) Look up ataraxia at Dictionary.com
also Englished as ataraxy, "calmness, impassivity," c.1600, from Modern Latin, from Greek ataraxia "impassiveness," from a-, privative prefix, + tarassein (Attic tarattein) "to disturb, confuse," from PIE root *dher- (1) "to make muddy, darken."