properly only an opening in a house or other structure for the admission of light and air, covered with lattice-work, which might be opened or closed (2 Kings 1:2; Acts 20:9)
The spies in Jericho and Paul at Damascus were let down from the windows of houses abutting on the town wall (Joshua 2:15; 2 Corinthians 11:33).
The clouds are metaphorically called the “windows of heaven” (Genesis 7:11; Mal. 3:10).
The word thus rendered in Isaiah 54:12 ought rather to be translated “battlements” (LXX, “bulwarks;” Revised King James Version, “pinnacles”), or as Gesenius renders it, “notched battlements, i.e., suns or rays of the sun”= having a radiated appearance like the sun.