[{"Bold_text": "noun", "List Items": ["Electricity.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.", "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."]}]