pendulum

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A body suspended from a fixed support so that it swings freely back and forth under the influence of gravity, commonly used to regulate various devices, especially clocks. Also called simple pendulum.
2. n. Something that swings back and forth from one course, opinion, or condition to another: the pendulum of public opinion.

Century Dictionary and Cyclopedia

1. n. Anything that hangs down from a point of attachment and is free to swing.
2. n. In mech., a body so suspended from a fixed point as to move to and fro by the alternate action of gravity and its acquired energy of motion. The time occupied by a single oscillation or swing is counted from the time of the descent of the pendulum from the highest point on one side till it attains the highest point on the opposite side. This time is called the period of oscillation of the pendulum. A simple pendulum in the mechanical sense is a material particle suspended by a weightless rod and moving without friction. A single weight attached by a string, etc., approximates to an ideal simple pendulum. The period of oscillation of a simple pendulum in vacuo is
3. n. A chandelier or lamp pendent from a ceiling.
4. n. A guard-ring of a watch and its attachment, by which the watch is attached to a chain.
5. n. A pendulum that at some point of its path closes a circuit, this in turn either reporting the beats of the pendulum at distant stations for time-comparisons, or directly controlling a number of clocks. See electric clock, under clock.
6. n. See the adjectives.
7. n. A pump in which the reciprocating motion of the piston is controlled by a pendulum.
8. n. A pump the handle of which swings on either side of its center of suspension.
9. n. A pendulum consisting of a spherical bob suspended from a cord or wire.

Wiktionary

1. n. A body suspended from a fixed support so that it swings freely back and forth under the influence of gravity, commonly used to regulate various devices such as clocks.

GNU Webster's 1913

1. n. A body so suspended from a fixed point as to swing freely to and fro by the alternate action of gravity and momentum. It is used to regulate the movements of clockwork and other machinery.

WordNet 3.0

1. n. an apparatus consisting of an object mounted so that it swings freely under the influence of gravity