compersion

Coined in the early 1990s by a group of members of the Kerista Commune, a polyamorous group based in San Francisco, California, U.S.A., in existence between 1956 and 1991, apparently randomly using an alphabet board (similar to a Ouija board), with -ion (suffix forming nouns). The hypothesis that the word is derived from French compère (“partner”) + English -sion (a variant of -tion (suffix forming nouns)), based on an earlier use of French compérage by the French anthropologist and ethnologist Claude Lévi-Strauss (1908–2009) to denote the practice of brothers-in-law sharing wives observed among Tupi people of the Brazilian Amazon, is less plausible: a website run by former members of the community states that neither the word compérage nor Lévi-Strauss’s work was known to them at the time, and the formation of the word in this way does not correspond to any known morphological process.

来源：wiktionary