As a Noun: 1. The ceremony in which a person is immersed in water as a sign that they have become a member of a Christian Church. English = baptism. 2. A person who is a Christian who believes that baptism is necessary for a Christian, and that it should happen only to someone who is old enough to understand what they are doing. English = Baptist. As a Verb or Adjective: 1. To immerse someone in water as a sign that they have become a member of a Christian Church. English = baptise.