means A hinged or sliding door set into a floor, ceiling, or stage that opens to reveal a hidden passage or drop below.

from A plain English compound of 'trap' and 'door.' 'Trap' descends from Old English 'træppe,' a snare or device for catching prey — the same root behind trapping animals. The 'door' here is literally a door, so a trapdoor began as any door that worked like a trap: concealed, sprung, swallowing whatever stepped on it. The word stretched naturally to stage trapdoors, ship hatches, and the gallows' fatal drop.