Other forms: letterboxes
A letterbox is the box or slot where the post lands at your house. Through the letterbox, a letterbox flap, check the letterbox.
British houses have a slot in the door and American ones a box at the road, which is why post is delivered to the hall in one country and the kerb in the other. Letterbox format is also a way of showing a wide film on a square screen.
1nounletterboxThe box or slot where the post lands at your house.
“The newspaper dropped through the letterbox and landed on the mat.”
letterbox is a box.
Also accepted in games: mailbox, postbox
Letter plus box, from the nineteenth century, when the penny post made a door slot worth cutting.
From letter + box.
Etymology from Wiktionary, CC BY-SA