1. To be based on facts and on things that really have happened and are not invented. English = (be) true, (be) factual, (be) real.
2. To have no doubt that something is in agreement with the facts, to have no doubt that something is true. English = (be) sure, (be) certain.
3. To be firm and clear, and be unlikely to be changed. English = (be) definite.
4. To believe that someone is honest, is telling the truth and will not deliberately do anything to harm you. English = trust.