compersion

Coined by Kerista Community on 28 November 1980 during an alphabet (like Ouija) board session by a group of 15 members of the community. They asked "Can we have a word that describes the emotion that is the antonym of jealousy?" The Kerista community practiced polyfidelity, a form of ethical non-monogamy with fidelity to the group. The answer was "compersion".
A derivation from the root of the Latin verb partior (“to divide, to share”) + prefix com- (“with”).
Another hypothesis that it may be derived from French compère (“partner”) + -sion, based on an earlier use of the French compérage to denote the practice of brothers-in-law sharing wives observed among Tupi people of the Brazilian Amazon, is less plausible: not only does it not correspond to any known morphological process, but a website run by former members of the community clearly states that neither the word compérage nor Lévi-Strauss's book were known to them at the time.