from
The Collaborative International Dictionary of English v.0.48
mousetrap \mouse"trap`\, mouse trap \mouse" trap`\, n.
Any device that catches, and usually kills, mice. They are of
various designs, the most common being a stiff loop of wire
mounted on a small wooden platform base and attached to a
strong spring, which holds the loop firmly against the base.
To activate the trap, the loop is pulled through a 180[deg]
arc against the tension of the spring and held against the
base by a delicate metal catch, which can keep the loop from
moving, though in a state of high tension. The metal catch is
moved when a mouse tries to take a piece of bait attached to
it, releasing the loop which forcefully moves though an arc,
usually killing the mouse. A larger version of the same
device is used as a {rat trap}.
[1913 Webster]