Pendulum
1. A pendulum is a weight suspended from a pivot so that it can swing freely.
2. The pendulum of a clock is a rod with a weight at the end which swings from side to side in order to make the clock work.
When a pendulum is displaced sideways from its resting, equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position. When released, the restoring force acting on the pendulum's mass causes it to oscillate about the equilibrium position, swinging back and forth. The time for one complete cycle, a left swing and a right swing, is called the period. The period depends on the length of the pendulum and also to a slight degree on the amplitude, the width of the pendulum's swing.
Pendulums are also used in scientific instruments such as accelerometers and seismometers. Historically they were used as gravimeters to measure the acceleration of gravity in geo-physical surveys, and even as a standard of length. The word pendulum is new Latin, from the Latin pendulus, meaning hanging.
Merriam-Webster's Collegiate® Dictionary, Eleventh Edition https://www.merriam-webster.com/dictionary
The free dictionary https://www.thefreedictionary.com/
Britannica https://www.britannica.com/science/