pendulum

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun 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.
• noun Something that swings back and forth from one course, opinion, or condition to another.

from The Century Dictionary.

• noun Anything that hangs down from a point of attachment and is free to swing.
• noun 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.
• noun A chandelier or lamp pendent from a ceiling.
• noun A guard-ring of a watch and its attachment, by which the watch is attached to a chain.
• noun 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.
• noun See the adjectives.
• noun A pump in which the reciprocating motion of the piston is controlled by a pendulum.
• noun A pump the handle of which swings on either side of its center of suspension.
• noun A pendulum consisting of a spherical bob suspended from a cord or wire.

from the GNU version of the Collaborative International Dictionary of English.

• noun 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.
• noun See under Ballistic.
• noun a clock pendulum in which the effect of changes of temperature of the length of the rod is so counteracted, usually by the opposite expansion of differene metals, that the distance of the center of oscillation from the center of suspension remains invariable; as, the mercurial compensation pendulum, in which the expansion of the rod is compensated by the opposite expansion of mercury in a jar constituting the bob; the gridiron pendulum, in which compensation is effected by the opposite expansion of sets of rods of different metals.
• noun an ordinary pendulum; -- so called, as being made up of different parts, and contrasted with simple pendulum.
• noun a weight connected by a rod with a fixed point; and revolving in a horizontal circle about the vertical from that point.
• noun the weight at the lower end of a pendulum.
• noun a plumb level. See under Level.
• noun the balance of a watch.
• noun an imaginary pendulum having no dimensions except length, and no weight except at the center of oscillation; in other words, a material point suspended by an ideal line.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun 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.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an apparatus consisting of an object mounted so that it swings freely under the influence of gravity