Apathy. From the Greek apatheia, meaning "not-suffering". In the sense in which it was used by the Stoics, it refers to a state of mind in which one has complete serenity and peace. It has a counterpart among the Epicureans, which they emphasized under the name of ataraxia. The notion is very similar to the serenity that is so highly valued in Buddhist attitudes.

Geddes MacGregor, Dictionary of Religion and Philosophy, New York: Paragon House, 1989

apathy : (f.) upekkhā; udasīnatā.

A.P. Buddhadatta Mahathera, Concise Pali-English and English-Pali Dictionary [available as digital version from Metta Net, Sri Lanka]