booby trap
A booby trap is a form of trap that is intended to physically harm, kill, or surprise the victim that falls into it rather than capture or restrain them. A booby trap may be baited to draw the target into triggering the trap.
Booby traps are an extremely common trope in adventure and fantasy settings - where a character may be exploring a dungeon, tombs, ancient ruins, or a creepy castle - a hidden button, pressure plate, or rigged chest may trigger swinging pendulum blades, arrows shooting out of walls, giant boulders meant to crush the target, sharpened sticks that shoot out of the floor, or cause the floor to open, revealing a pit full of spikes or stakes. Booby traps are also used in warfare, landmines can be considered a booby trap when planted. "Booby trap" can also apply to a practical joke that relies on surprising and fooling the target.
Note
Despite the name, this tag has nothing to do with breasts (unless the trap is hidden in someone's cleavage) - "booby" is a term for a "fool" or "stupid person" - if a character is trapped by another character's breasts, trapped and between breasts, head between breasts, face in breasts and/or breast smother are the tags to use.