a marriage in which the partners agree that each is free to have sexual relationships with other partners.
Origin of open marriage
First recorded in 1970–75
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
a marriage in which the partners are free to pursue their own social and sexual lives
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012