from
The Collaborative International Dictionary of English v.0.48
Commutator \Com"mu*ta`tor\, 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]