'Thick Cloud' in the Bible

And the LORD said unto Moses, "Lo, I will come unto thee in a thick cloud, that the people may hear when I talk with thee, and also believe thee forever." And Moses showed the words of the people unto the LORD.

And the third day in the morning there was thunder, and lightning and a thick cloud upon the mount, and the voice of the horn waxed exceeding loud, and all the people that was in the host was afraid.

And the people stood afar off, and Moses went into the thick cloud where God was.