An opening, as in the deck of a ship, in the roof or floor of a building, or in an aircraft.
The cover for such an opening.
A hatchway.
Nautical A ship's compartment.
The hinged rear door of a hatchback.
A floodgate.
down the hatch
Drink up, as in "Down the hatch," said Bill, as they raised their glasses. This phrase, often used as a toast, employs hatch in the sense of "a trap door found on ships." [Slang; c. 1930]