Deadlight

Noun

1. A strong (often wooden) shutter fitted over a porthole, that can be closed in bad weather to keep water out and discourage the glass windows from breaking.
2. A deck prism, a device to allow light into the cabin of boat through the deck.
3. An eye.
4. An eyelid.
5. This term needs a definition. Please help out and add a definition, then remove the text {{rfdef}}.