宗教 religion adj.（形容詞） believer（~教徒） founder（開祖）
無神論 atheism atheist atheist（無心論者）
神道 Shinto, Shintoism Shinto Shintoist
ヒンドゥー教 Hinduism Hindu Hindu (older than Buddhism)
仏教 Buddhism Buddhist Buddhist Budda(~486BC or 386BC)
ユダヤ教 Jewish Jewish Jew (Jehovahﾔﾊｳｪ､ｴﾎﾊﾞ)
キリスト教 Christianity Christian Christian(s) Christ
カトリック教 Catholicism Catholic Catholic
プロテスタント教Protestantism Protestant Protestant
イスラム教 Islam Islamic Islamite Muhammad(~632)
（回教） Muhammadanism Muhammadan Muhammadan
シーア派 Shiah, Shia, Shiism Shiah, Shia Shiite
スンニ派 Sunnism Sunni, Sunnite Sunni, Sunnite
イスラム原理主義 Islamic fundamentalism
儒教 Confucianism Confucian Confucian(ist)(儒者）Confucius(~479BC)
Polytheism 多神教 Monotheism 一神教
Theism 有神論 Atheism 無神論
八百万の神（やおよろずのかみ）・・・so many (or all) kinds of God / a concept for God in Shintoism
We Japanese sometimes pray to so many kinds of God for something. I think this is one of the most outstanding points to express the Japanese way of thinking on God.
The Japanese is said to be a race not to adhere to a religion. But when we are alive, we have followed various customs related to Shinto such as Omiyamaeri (when a baby was born) and Shichigosan (when a child is 3, 5, 7 years old). While after a person die, we have a tendency to follow Buddhism customs such as Syonanoka (6 days after a person died) and Jyuunanakaiki (16 years after a person died).
I learned at the university that when we think over religion, it is also important to think about religious ceremonies and festivals concerned.