Definition of "commutator" [com•mu•ta•tor]

• A cylindrical arrangement of insulated metal bars connected to the coils of a direct-current electric motor or generator, providing a unidirectional current from the generator or a reversal of current into the coils of the motor. (noun)
• Mathematics In a commutative or noncommutative group, an element of the form ghg-1h-1 where g and h are elements of the group. If g and h commute, the commutator is the identity element. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "The next steps were to first turn on the petrol, secondly, to switch on the ignition, next to see that the lever to the commutator is retarded as far as possible."
• "The mechanical reversal of the current is accomplished by the use of the commutator, which is a metal ring split into halves, well insulated from each other and from the shaft."
• "These tubular sections are called the commutator plates."