noun
trapdoor; flap door
A door set into a floor, ceiling, or roof that opens by dropping or swinging down.
舞台には落とし戸が仕掛けてある。
The stage is fitted with a trapdoor.
屋根裏へ上がる落とし戸を開けた。
I opened the trapdoor leading to the attic.
Compound of 落とし (dropping) + 戸 (door).