The Buddhist word for it was upekkha. The Muslims spoke of aslama. The Hebrews, hishtavut. The second book of the Bhagavad Gita, the epic poem of the warrior Arjuna, speaks of samatvam, an “evenness of mind—a peace that is ever the same.” The Greeks, euthymia and hesychia. The Epicureans, ataraxia. The Christians, aequanimitas.
