Custom of having many wives

Solution (By Examveda Team)

One word substitute is Polygamy.

Monogamy: the practice of marrying or state of being married to one person at a time.
Bigamy: the offence of marrying someone while already married to another person.
Polygamy: the practice or custom of having more than one wife or husband at the same time.
Matrimony: the state of being married; marriage.