pantagamy (n.)

"communistic group marriage," in which every man in the group is regarded as equally the husband of every woman in it and vice versa; especially as practiced at in mid-19c. Perfectionist communes such as that of Oneida, New York; 1852, from Greek pantos "all" (see pan-)  + -gamy "marriage." A malformation, it would properly be *pantogamy; as pant- was the short form of the Greek word before a vowel, and Greek agamy was "celibacy," the modern word would literally mean "celibacy of all."