skylight

noun4

1. •
   A window, dome, or opening in the roof or ceiling, to admit natural light.
2. •
   A hole in the upper part of a lava tube, yielding a view of the lava within.
3. •
   Diffuse sky radiation—solar radiation reaching the earth's surface after having been scattered from the direct solar beam by molecules or suspensoids in the atmosphere.
4. •
   A region of flat, thin ice allowing a submarine to surface.