deadlight

noun Nautical.

1. a strong shutter able to be screwed against the interior of a porthole in heavy weather.
2. a thick pane of glass set in the hull or deck to admit light.

noun

1. nautical
   1. a bull’s-eye let into the deck or hull of a vessel to admit light to a cabin
   2. a shutter of wood or metal for sealing off a porthole or cabin window
2. a skylight designed not to be opened