reveal, revealed, revelation

Definition:

The term "reveal" means to cause something to be known. A "revelation" is something that has been made known.

God has revealed himself through everything he has created and through his communication with people by spoken and written messages.
God also reveals himself through dreams or visions.
When Paul said that he received the gospel by "revelation from Jesus Christ," he means that Jesus himself explained the gospel to him.
In the New Testament book "Revelation" is about God revealed events that will happen in the end times. He revealed them to the apostle John through visions.

Other ways to translate "reveal" could include "make known" or "disclose" or "show clearly."
Depending on the context, possible ways to translate "revelation" could be "communication from God" or "things that God has revealed" or "teachings about God." It is best to keep the meaning of "reveal" in the translation.
The phrase "where there is no revelation" could be translated as "when God is not revealing himself to people" or "when God is not speaking to people" or "among people whom God has not communicating."