'Dense' in the Bible

The Lord said to Moses, "I am going to come to you in a dense cloud, so that the people may hear when I speak with you and so that they will always believe in you." And Moses told the words of the people to the Lord.

On the third day in the morning there was thunder and lightning and a dense cloud on the mountain, and the sound of a very loud horn; all the people who were in the camp trembled.