extension cord vs multiplug

extension cord

noun
  • An electrical cord with a plug one end, and a single socket or a multi-port socket at the other end, used for powering one or more devices at a distance, too far from the wall outlet to be reached by the normal cords of the device or devices. 

multiplug

noun
  • An electric device that allows more than one plug to connect to a single socket by containing multiple similar sockets; particularly for mains electricity. 

How often have the words extension cord and multiplug occurred in a corpus of books? (source: Google Ngram Viewer )