Christianity (noun)

1. The religion based on the person and teachings of Jesus of Nazareth, or its beliefs and practices.
2. The belief in the one God, in Jesus as the Messiah, and in the Holy Spirit.

Origin:

Late middle english: from old french chrestien "follower of christ", from latin christianus, from christus (see christ).

Examples:

1. He practiced Christianity.
2. She converted to Christianity.
3. The religion of Christianity has many different denominations.
4. The impact of Christianity on Western culture is undeniable.
5. He studied the history of Christianity.