commutator

1 :  a series of bars or segments connected to the armature coils (see armature 2b)of a generator or motor so that rotation of the armature will in conjunction with a set of fixed brushes (see ²brush 3) convert alternating current into direct current ◆In a generator, a commutator results in an output of direct current. In a motor, the commutator converts incoming alternating current into direct current before using it to generate motion.

2 :  an element of a mathematical group that when used to multiply the product of two given elements either on the right side or on the left side but not necessarily on both sides yields the product of the two given elements in reverse order