*commutator*

n. (Elec.) A piece of apparatus used for reversing the direction of an electrical current; an attachment to certain electrical machines, by means of which alternating currents are made to be continuous or to have the same direction. It may be attached to the end of the spindle of an electric motor, where a brush is in contact sequentially with the parts of the spindle that conduct current to the different windings of the motor. [ 1913 Webster +PJC ]