It's the 4-syllable practice of having more than one spouse at the same time
I think it's a little unfair to now tag on 
polyprogenetive in your answer, after I posted ... sumlic Mar 17 '15 at 4:57... [DOC] [TLE] vocabulary - What is a word called that has more than one syllable ... [PAR] Aug 13, 2010 ... What is the correct term for a word that has two or more syllables, e.g.