DEADLIGHT
deadlight
(noun) a strong shutter over a ship’s porthole that is closed in stormy weather
Source: WordNet® 3.1
Etymology
Noun
deadlight (plural deadlights)
(nautical) 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.
(nautical) A deck prism, a device to allow light into the cabin of boat through the deck.
(figurative) An eyelid.
Source: Wiktionary
Dead"light`, n. (Naut.)
Definition: A strong shutter, made to fit open ports and keep out water in
a storm.
Source: Webster’s Unabridged Dictionary 1913 Edition