Polygamy (from Late Greek πολυγαμία, polygamía, state of marriage to many spouses) is the practice of marrying multiple spouses. When a man is married to more than one wife at the same time, sociologists call this polygyny. When a woman is married to more than one husband at a time, it is called polyandry.

What is first wife called?

It is usually not used for a person who died while being the wife. So the former wife would be a divorced wife, with no indication whether that former wife is alive or dead. So if Joe marries Jane, she dies, and he marries Joanne, then you would call Jane his first wife, but probably not a former wife.