Christianity - 1. the Christian religion, including the Catholic, Protestant, and Eastern Orthodox churches. 2. Christian beliefs or practices
Christianity is monotheistic, meaning that Christians believe that only one God exists.
Polytheism - the doctrine of or belief in more than one god or in many gods.
Mormonism is polytheistic, because Mormons believe that there are countless gods. The definition does not require the worship of those gods, only a belief in their existence.
Polygamy - the condition or practice of having more than one spouse at a time.
Polygyny - the condition or practice of having more than one wife at a time.
Although the Mormon Church has discontinued the promotion and teaching of polygamy, it has never declared it a false doctrine nor rescinded it as a necessary step to achieve godhood.