The Cambridge Dictionary defines "polygamy."
"Polygamy," Cambridge Dictionary, accessed May 1, 2023
polygamy
noun [ U ]
US /pəˈlɪɡ.ə.mi/ UK /pəˈlɪɡ.ə.mi/
the fact or custom of being married to more than one person at the same time
Compare
bigamy
monogamy
polyamory
polygamy
noun [ U ]
US /pəˈlɪɡ·ə·mi/
the custom or condition of being married to more than one person at the same time