ataraxia (n.)

often Englished as ataraxy, c. 1600, "calmness, impassivity," a term used by stoics and skeptics, from Modern Latin, from Greek ataraxia "impassiveness," from a- "not, without" (see a- (3)) + tarassein (Attic tarattein) "to disturb, confuse," from PIE root *dhrehgh- "to confuse." It seems to have been disused; when ataraxia appeared in print in English in 1858 it was regarded as a neologism.