a device for reversing the direction of a current.
(in a DC motor or generator) a cylindrical ring or disk assembly of conducting members, individually insulated in a supporting structure with an exposed surface for contact with current-collecting brushes and mounted on the armature shaft, for changing the frequency or direction of the current in the armature windings.
Mathematics. the element equal to the product of two given elements in a group multiplied on the right by the product of the inverses of the elements.

1830–40; commutate + -or2 Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
commutator (ˈkɒmjʊˌteɪtə)
1.  a device used to reverse the direction of flow of an electric current
2.  the segmented metal cylinder or disc mounted on the armature shaft of an electric motor, generator, etc, used to make electrical contact with the rotating coils and ensure unidirectional current flow

Collins English Dictionary - Complete & Unabridged 10th Edition
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Word Origin & History

1839, agent noun from L. commutare (see commute).
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Science Dictionary
commutator   (kŏm'yə-tā'tər)  Pronunciation Key 
  1. The arrangement of contact points in an electric motor connecting an external direct current power supply and the rotating electric coils that use the power, used to generate the AC voltages needed by the coils. The commutator is located at the rotating shaft of the motor, where two power contacts are swept underneath two metal brushes, supplying positive and negative voltage to the coils. When the motor has rotated 180 degrees, the power contacts are each moving under the opposite brush, reversing the polarity of the voltage supplied to the coils.

  2. In a group or an algebra, an element of the form ghg-1h-1 where g and h are elements of the group or algebra. If g and h commute, the commutator is the identity element. The commutator is often written [g, h].

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Example sentences
Furiously he tested the spark-plugs, stared at the commutator.
They never catch up because of the switching action of the commutator.
Some alternators have commutator and brushes, and others are solid-state.
Check and clean rotor and stator, check and clean commutator and slip rings per manufacture recommendations.
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